Apparently, both Antonio Fabiani AND Leonardo Cardinale of Ashita no Nadja, in regards to the same girl: Julietta Satori.
Canon-wise, Greece from Axis Powers Hetalia might be this toward Japan, although his promiscuity isn't really his main character trait (apparently you can still be an all-around Nice Guy even if you have the honor of being at the top of sex frequency charts).
Fanon-wise, France is often depicted as this in fanworks where he's paired with someone, especially if it's with Canada.
In The Wallflower manga, womanizer Ranmaru is very clearly falling in love with his arranged fiancee Tamao (a commitment he originally tried to get out of), even if he hasn't fully realized it yet.
In Hot Gimmick, Hatsumi's younger sister Akane is known as the 'easiest' girl around in school, to the point where when she thinks that she's pregnant, she can't decide which one of her boyfriends could have knocked her up. Later on, however, she finds herself falling for Hatsumi's sweet and unassuming friend Subaru, decides to Give Geeks a Chance, and the two end up as the series' Beta Couple.
In some Hana Yori Dango continuities, the F4's resident Casanova Soujiro falls for Tsukushi's best friend Yuki.
In ...Virgin Love, Daigo becomes this after meeting Kaoru. Kaoru also qualifies as a mankiller (maneater?) in love when he finally comes around.
Yuki from Gravitation reportedly had numerous one-night stands with women before meeting Shuichi. There's also the fact that he was reluctant to let himself love again after his first love Kitazawa set him up to be gangraped and he shot him dead in self-defense, until Shuichi helps him overcome it.
Chizuru for Azumi in Hen.
In Happy Yarou Wedding, former "King of the Night" Akira Todou falls in love with his housekeeper/nanny.
Ryo Saeba, the protagonist of City Hunter, is a notorious and successful casanova in spite of his job as a Professional Killer, and is in love with his partner Kaori, even if he doesn't want to admit it.
Gambit and Rogue of X-Men are a little different than the standard — she accepts that he has genuine feelings for her, but since her powers mean they can't touch each other ever, she wishes he'd stop pursuing her and reminding her of what she can't have. There have been some hints of the two trying therapy to get around this problem, but, naturally, it hasn't worked — "Bizarre Love Triangle" is an excellent example, where despite Emma Frost's psychic therapy sessions, an attempted makeout session nearly kills Gambit.
Naveen: I am having troubles. Ray: Ya got that right, bro. You in love. Naveen: I know. It is horrible! Ray: But it's the good kind of horrible. Naveen: I have courted many thousands of the most beautiful women in all of the world. But this girl, Tiana, she has taken my heart and... and... Ray: Yeah, that's love, alright.
Despite Tramp's escapades with Lulu and Fifi and Trixie - not to mention Rosita Chiquita Juanita Chihuahua - he eventually falls for Lady in Lady and the Tramp.
This is the plot for the Heath Ledger version of Casanova.
Valmont from Dangerous Liaisons. However, it's arguably Deconstructed — he continues to sleep around and ultimately leaves the woman when asked to by his partner in Unholy Matrimony. He comes to regret it and instead of making things better, he decides to get himself killed.
The Vince Vaughn character (and to a degree the Owen Wilson character) in Wedding Crashers.
Ewan McGregor's character in the '60s rom-com pastiche Down with Love is a womanizing journalist (or "Lady's man, man's man, man-about-town") who ends up falling in love with Barbara (Renee Zellweger), the independent, modern-minded author of the eponymous feminist manifesto who seemingly wants nothing to do with him.
The 70's Australian sex comedy Alvin Purple. The title character is irresistible to women, but falls in love with the one who's immune to his charms.
Tony Stark from Iron Man. A filthy rich, brilliant, narcissistic casanova who is clearly in love with his long-time (and much beleaguered) assistant Pepper Potts.
A plot point in The A-Team movie is that Face and Lt. Sosa are former lovers. We find out later that she dumped him because he finally wanted a real relationship and she didn't.
Face: You knew I was a player, and you wanted to play. Then I wanted to get serious and you couldn't handle it.
Adam Sandler's character in 50 First Dates lives a life of one-night stands, then falls for an amnesiac girl who forgets each day when it's finished.
Made extra ironic by the fact that this is the first girl he's wanted a real relationship with and all he can have with her is a single day at a time.
Averted in Hitch, where the eponymous character can be a ladykiller, but he is actually very much pro-love. His job involves being the icebreaker for shy guys who want to engage in a long-term relationship. A memorable scene involves a guy who just wants Hitch's help in getting a one-night stand, so Hitch simply leaves after nearly breaking the guy's arm. Unfortunately for Hitch, his Love Interest assumes he really does help guys get one-night stands and ends up ruining his career.
Loveless in Los Angeles has a guy get fed up with pining over a Just Friends women in college after she gets engaged to someone else when he was about to do his Love Confession. This gives him a Freudian Excuse to become a Lady Killer, but then his old flame re-enters the picture, freshly divorced.
Subverted in Don Jon. Jon wants to believe that this is true of his relationship with Barbara, but he really objectifies her just as much as his other sexual partners.
Kalten in the Tamuli series by David Eddings. Particularly funny is that he can't seem to realize the girl he likes is in love with him. Of course, what with this being a David Eddings series, as soon as said girl finds out, she clears that right up. Expressively.
Spider in Anansi Boys has godlike powers he uses to seduce women by the dozens. However, when he falls in love with Rosie while impersonating his brother Charlie, he realizes that he doesn't want to force her to love him; he wants her to love him as he is, which means admitting to her who he really is.
Kate Daniels' love interest Curran runs into this problem when trying to court the heroine. The fact that he's had a "parade" of girlfriends doesn't help his case at all, nor does the fact that he has an ego and hates to hear the word "no".
Kate: "And be girlfriend number twenty-three soon to be dumped in favor of girlfriend number twenty-four who has slightly bigger boobs? I don't think so."
Same with her best friend Andrea and her love interest Raphael.
Don't let the marriage fool you though, he fully intends to keep drinking and gambling. His... insistance on reminding everyone of that fact is succinctly put by the ever stoicallyhilarious Talmanes:
"'So I believe you've told me,' Talmanes said.'Three or four times so far. I half believe that if I were to peek into your tent at night, I'd find you mumbling it in your sleep. 'I'm going to keep bloody gamling! Bloody, bloody gambling and drinking! Where's my bloody drink? Anyone want to gamble for it?''"
Henry Crawford of Mansfield Park claims to be this, but the heroine doesn't trust he can give up his ladykilling ways. She's right.
In Gone with the Wind, Scarlett takes great pleasure in flirting with any man that crosses her path, even ones who are already taken, but she has her heart set firmly on Ashley. It later turns out that the man she truly loved was not Ashley but Rhett (who is also this trope towards her), but she realizes thisa little too late.
In Tales of the Frog Princess, PrinceGarrid, who's been described as a ladies man, two-times Li'l and PrincessHazel (Li'l is the more sympathetic of the two, since she genuinely falls for him) by courting Hazel, but meeting Li'l, and "forgetting" to mention it. When Li'l finds out she (rightfully) leaves him. He shows up later, admitting to have fallen in love with her.
The Anne of Green Gables series has Gilbert Blythe, who was wont to tease and play with the affections of the girls in his class. However, after he tries his usual tricks on Anne Shirley and gets a slate smashed over his head for his trouble, he falls head over heels for her. From then on, to the other girls' massive frustration, he has eyes for no one else.
Kenneth Ford, the Love Interest of Anne and Gilbert's youngest child, Rilla, is this, too, though it's not as clear.
In Howls Moving Castle, Howl is a vain and literally heartless flirt, pursuing women passionately and then losing interest after they give in. Sophie does notice when this behavior starts to change; she just totally fails to realize that she's the reason.
Dex is eventually this for Emma in One Day though it takes him a fair few years and many failed relationships to realise it.
Nealan of Queenscove, from Tamora Pierce's Protector of the Small, has various crushes throughout the quartet on multiple noble ladies, up to and including the Queen. He has a tendency to make quite a lot of noise about these, writing (terrible) poetry and mourning to all and sundry the fact that all his crushes are hopelessly unrequited. However, when he falls in love with Yukimi noh Daiomoru, he is so tight-lipped about it that even his best friend Keladry of Mindelan has no clue how he feels about her until he faces his Ordeal. They end up Happily Married.
The first Red Dwarf novel establishes that Dave Lister is perfectly comfortable with going out and seducing women as long as he's not too keen on them. When he is keen he has "the wit, charm and self-possession of an alsatian dog after a head-swap operation". As in the TV show he falls in love with the out-of-his-league officer Kristine Kochanksi and promptly forgets all about any of his previous relationships.
In Of Fear and Faith, Aiden, who is known to sleep with literally every attractive woman that crosses his path, falls in love with Lilac at first sight and doesn’t know how to deal with it. He goes from shameless flirting to awkwardly distancing himself from her to genuine concern for her happiness and safety back to shameless flirting. Obviously, he Cannot Spit It Out.
Similar to the above example, Ricky of Noah's Arc once he falls in love with Junito (he considers breaking his promiscuous ways, but it never pans out for long).
Owen Harper of Torchwood, the series' Kavorka Man, falls for a 1950s aviatrix who slips through a rift in time and, after a week-long affair and Owen's stumbling confession of love, flies right back through the rift and out of his life.
Jack Harkness counts as this - beginning as a character in Doctor Who, he was pretty much a con-artist who flirted with anything. Then he gets picked up by Rose and the Doctor, falls head over heels for the latter and ends up waiting for him to show up again for over one hundred years after they're separated. In the meantime he reworks the Torchwood Foundation from the ground up, removing a lot of the evil "in the Doctor's honour". He also gets madly flustered when trying to ask Ianto on a date in Torchwood and was married at some point.
Barney Stinson, quoted above from How I Met Your Mother. Sort of a subversion since he doesn't tone down his promiscuity at all (although he tries) for the sake of his new found love (at least until they actually get together).
Joey on Friends had a brief thing for Rachel. However, it really started back when the girls practically threw one of his girls of the week at him and he realized what the rewards of a relationship could be.
Shane from The L Word. Multiple times, as it never lasts.
In Kamen Rider Kiva, Otoya falls in love with Yuri. However, he ultimately falls in love with Maya, and Yuri ends up marrying another man off-screen.
Done in the Grand Finale of Night Court, where Dan vows to give up his Kavorka Man ways and earnestly pursue his dream woman, Christine. (It should be noted that Dan confesses this to Harry, not Christine.)
In season four of NCIS, Tony DiNozzo finds himself in this position with Jeanne Benoit, with the added complication that he initiated the relationship as part of an undercover operation and was never supposed to actually fall in love with her.
Samantha on Sex and the City has fallen in love a few times over the series run. In the first season it was with James, but she was dismayed when he had a really small penis; second time was with Richard who she finds herself actually wanting a monogamous relationship with (she complains to her friends "I think I caught monogamy! I must gotten it from YOU people!"); and finally with Smith who broke through more of her emotional barriers than any other guy she fell in love with.
Steven Hyde of That '70s Show when he falls in love with Jackie Burkhart. Prior to this he had been sleeping around, and was proud of never having formed any real attachments (even when he did have a thing for Donna). They maintain the relationship throughout several seasons, despite many setbacks involving Jackie's ex (and Hyde's best friend) Michael Kelso, and even break up several times due to Jackie's desire to get married one day. They finally find a resolution when Jackie is offered a job in Chicago, so she gives Hyde an ultimatum to propose or she will leave. He initally says no, so she leaves for Chicago, but Hyde follows her, another example of his actually being in love with her. When he gets there he finds Kelso already there with her and dressed only in a towel. This ends their relationship and Hyde goes back to sleeping around.
Brendan Brady prides himself on not getting to invested in his conquests, but that all changes when he falls hard in love with Ste Hay on Hollyoaks.
Patrick, when he starts seeing Sally in later seasons of Coupling.
Happened to Chuck on Gossip Girl, who fell in love with Blair. When she denied him he found himself unable to perform with other women (thus deciding to use her as "sexual Drano" which didn't go so well). He bounced back and started sleeping around again, until he and Blair actually became a couple.
Parodied on Saturday Night Live (of course) in a Ladies Man sketch in which Leon announces that he is in love and off the market. It turns out that his dream woman is an undercover cop... played by The Rock... who is, even in-universe, very and obviously male (much to Leon's obliviousness).
Played straight in The Movie where Leon falls for a woman and ends the story married with a child, but still doing his radio show.
A season one episode of Supernatural introduces us to DeanWinchester'sNew Old Flame Cassie. We get a glimpse of what Dean looks like in love, and it turns out he's kind of a sap. Sam has fun needling him about it until he realizes who dumped whom and why, and how badly Dean actually got hurt.
There's also Lisa, who first appeared in series 3 and came back for a handful of episodes in series 5 and 6, and while it's debatable whether Dean loved her or what she represented to him (a stable, 'apple pie' family life), he certainly abandons his promiscuity to be with her and cares for Ben like a true father.
Jack of Three's Company never fails to show up with a Girl of the Week, until the series finale where he's shown to settle down with his newest girlfriend Vicky. His friend Larry was also shown to seriously consider marrying one of his Girls Of The Week in one episode until Jack successfully talked him out of it (after discovering that said girl was actually a Stalker with a Crush for him).
Over the course of two seasons and roughly forty episodes, Rick Castle has fallen so hard for Kate Beckett that a) he has asked her to take care of his daughter should something happen to him, b) without hesitation, he calmly informed her that she was coming to live with him when her apartment got blown up, and c) the very sight of her kissing another man brought a look to his face that was so brokenhearted, fangirls cried. Yup, the guy's arse over teakettle, all right. For context, his Establishing Character Moment was autographing a woman's chest, he's been married at least twice, and he commands a decent price in celebrity bachelor auctions.
Nathan on One Tree Hill started as a Jerk Jock who'd do Anything That Moves. Then he fell in love with Haley, so in love that he not only reformed his ways but he married her in high school. Years later they're still married.
The Suite Life on Deck has a Kidanova example in Zack Martin, who early in season three fell head-over-heels for the new girl Maya, and vowed to reform his womanizing ways for her sake.
In the Japanese drama Nodame Cantabile, Dirty Old Man Stresemann had fallen in love with the school's principle when they were younger. But they decided to remain Just Friends after she was struck with an illness that stopped her from playing piano. Years later, visiting her and coming to the academy as a guest instructor, he chose to conduct her favourite song before he left from Japan. His feelings for her had never changed.
Kojo in Zeke and Luther developed feelings for Zeke's cousin Mia in the episode "Sludge".
Declan of Degrassi, known for flirting with other girls, falls hard for Holly J, who initially rejects his advances.
Santana from Glee. After a lot of sleeping around, including with Brittany, she realizes that Brittany is all she really wants.
In "Duets", Artie breaks off his pairing with Brittany when he thinks she seduced him just so he would sing with her. Turns out her affection was genuine after all.
Noah "Puck" Puckerman, having dated Quinn, Rachel, Mercedes, Santana and half the Cougars in Lima, finds himself falling head over heels, to the point of joining Celibacy Club because he wants to be less of an "I'm a Man I can't help it" type guy, for Lauren Zizes, President of the AV club and only girl on the school's wrestling team, because she's as much of a Bad Ass as him. She initially, despite being attracted to him, tells him they'll have to be Just Friends at first because "she needs to be wooed." And Puck - who formerly couldn't even get through an evening with Quinn without sexting Santana - is okay with this arrangement. In short - we have one Casanova who's found a love match!
ER's Doug Ross. Established from the first episode as a grade-A womanizer. . .who was desperately in love with Carol Hathaway.
Lee Stetson/Scarecrow of Scarecrow and Mrs. King gradually abandons his womanizing ways over the course of the series as he falls for (and eventually marries) Amanda King
Inverted by Quantum Leap. It's established early on that Al is a Chivalrous Pervert who eyes any woman he sees and has been married multiple times. Then in the episode "M.I.A.", he outright admits that his first wife Bethnote Who he "lost" because he was a POW for four years and she remarried in the meantime was the only woman he ever truly loved, and that he chases skirt in the hopes of finding someone who can mean as much to him. In the final episode Sam uses his "one free leap" to tell Beth not to give up on Al, which she does, and the closing text tells us that they're still Happily Married in 1999 and have had four daughters.
Logan Reese, from Zoey 101 seems to act like this after he starts dating Quinn, as he is not shown flirting with other girls after their First Kiss.
At first, Danny from Baby Daddy seems like the typical hockey player who Really Gets Around, but backstory reveals that he's been in love with Riley since high school, even when she was still "Fat Pants".
Don Draper from Mad Men in the Season 4 finale and all of Season 5.
Alex Karev of Grey's Anatomy is a contender for the long-term record. After eight seasons of bedding a different girl literally every week, he resolves to become a responsible, home-owner, resident-doctor type and stop seducing his interns. He promptly gets his heart broken by the next intern, who wants to be best buddies only.
One episode of Psych features Clive Prescott, a self-proclaimed "cad and deceiver" who has written books and teaches a class on the subject of ladykilling. He's believed to be romancing a rich widow to gain access to her money, until he reveals that he's romancing her because, to everyone's surprise, not the least his own, he has genuinely fallen in love with her.
Frasier: Bulldog falls in love in the episode "Love Bites Dog" only to end up heartbroken when the woman dumps him on the phone like he himself does with many of his one-night stands.
A few years later, Bulldog falls for Roz who also rejects him.
Assassin by John Mayer is about a ladykiller who falls for one of his many conquests. Unfortunately for him, she is only interested in a one night stand. "I was a killer was the best they've ever seen. I'd steal your heart before you ever heard a thing...little did I know that girl was an assassin too."
A musical example would be "Conquest" by Patti Page (later covered by the White Stripes).
Mecano's song La fuerza del destino ("The strength of Fate") depicts how a Casanova is at first peeved that his date denied him a kiss in the first date, but as time passes he comes to develop feelings for her.
"Fooled Around And Fell In Love" by Elvin Bishop.
Stealing My Heart by The Rolling Stones is all about this, containing lyrics like: "I was just out there to have me some fun / but it's easier said than done," and "I thought you were dinner, but you were the shark."
Neverwinter Nights 2: Mask of the Betrayer has Gannayev, an abnormally handsome hagspawn Casanova. As you get to know him better, it is revealed that he is unsatisfied with such an existence and is actually looking for "a dream that truly touched" him. Moreover, his cocky over-the-top attitude as well as the Casanova ways are a shield he puts up to mask his inner insecurity and fear of showing people who he really is. Needless to say, given the right treatment he strips away his pretensions and adapts a worshipping lovebird attitude toward the protagonist.
He's also totally devoted to her. In the PSP remake, he's the only male S link the new Gender Flip protagonist can't have a romantic relationship with. Despite the fact that she could finish the S-Link before he even knows of his love interest. Some shippers aren't happy.
Ryoji Mochizuki also qualifies as one if you pursue a romantic relationship with him. Despite the fact he's a constant flirt, he tells the female protagonist that she's the only girl he's ever loved after his S link is maxed.
Vico's romance arc in A Dance with Rogues. Also possibly gender-flipped with the player character.
Pretty much the whole deal behind YuushiOshitari's paths in the Prince of TennisDating Sims. Specially in Gakuensai no Oujisama, where the main girl Shizuka even gets to see him get bitchslapped by an old girlfriend.
Zidane Tribal, the protagonist of Final Fantasy IX, has this as a major part of his Character Development. He starts out as a fairly open skirt chaser (at the age of 16, no less), but then he falls for Garnet/Dagger, causing some emo-ness to ensue. Of course, in his case, it's made worse by the fact that Garnet's a princess, therefore supposedly not "reachable" for him even if he changes his ways. Doesn't stop them from getting together in the end, though.
Derek in RE: Alistair, if you get his ending. He gets bonus points for initially flirting with Merui solely to play with and emotionally string her along, only to admit developing genuine feelings for her when she confronts him about this.
Harvest Moon DS Cute: If you choose to go for Skye, a playboy thief. His lines get cheesier with each heart event.
Team Fortress 2 - Most of this plays out in the supplementary materials and Fanon, but it's pretty heavily implied that the relationship between the RED Spy and the BLU Scout's mother is this trope (his rival took a bunch of pictures of them on a date and then having steamy sex with each other, but the RED Spy only claimed one of them back for himself: the one showing him and his "petit cho-fleur" holding hands).
Part of the backstory of The Rogue, Lyndon, in Diablo III. Exactly how much SUCCESS he has with women is anybody's guess, but he's definitely eager to flirt with anything in a skirt... or a fur bikini... or a skimpy mage-robe... he's not picky, really, and doesn't even wince at being shot down. If you chastise him for his womanizing, he claims that he's only ever met one woman 'worth keeping'. Further digging into his past reveals that he originally turned to crime in order to fund his attempts to woo her, and that she wound up marrying his goody two-shoes brother instead. The pain in his voice is audible whenever she comes up in conversation, turning his otherwise Loveable Rogue demeanor bitter in a split second...
Bogey of Kid Radd. Sure, he always hits on her (and everyone else) because she's hot, but late into the comic he realizes he's actually fallen for Sheena, but only adds to his feelings of utter uselessness because he can plainly see that she and Radd are meant to be.
Slick from Sinfest shows genuine love for Monique, but is unable to express it properly. Of course he isn't a real ladykiller, but since he fancies himself one and still pursues the status, it qualifies.
Also, Fuchsia is a seductress devil who is showing deep feelings for Criminy.
Fox from Boy Meets Boy and Friendly Hostility flirts with Anything That Moves, until he develops a serious interest in his best friend Collin. Collin, fully aware of Fox's lecherous nature, initially refuses to play into his "game" until Fox bluntly tells him, "I'm not kidding around anymore, Collin." The two wind up in a stable and loving relationship that lasts for years, and Fox is genuinely heartbroken when Collin eventually breaks up with him.
Tip Wilkin of Skin Horse has this happen to him in the current story arc when he meets Mad Scientist Tigerlily Jones. He loses his superpower ability to make any woman fall into his bed, and even loses the ability to pick handcuffs with a bobby pin. Don't ask why he would need to.
Joe Rosenthal of the Walkyverse comics, whose defining trait is his blatant sexism and sexual magnetism, falls into this after finding love on an Internet forum and eventually settling into his first monogamous relationship with his crush. Said crush goes missing, however, and to cope with the loss he regresses deep into his old habits.
Boomhauer from King of the Hill. He manages to get women crawling all over him, even if they have only just seen him, and actively avoids getting into a serious relationship. But when he does actually fall in love, he gets a cruel and ironic backlash when the woman in question turns out to be using him even more cruelly than he ever used any other woman: she can't get his name right, can't understand half of what he's saying, and tells him, while he's kneeling on her doorstep after proposing to her, that "Actually, whenever you talk, I'm usually just nodding and smiling while waiting for your pants to come off." Can you say "Ouch"?
"Jerome is the New Black" reveals that Quagmire became a heartless sex hound because the one woman he truly loved (Cheryl Tiegs) dumped him, which plays this trope for drama and provides a Freudian Excuse as to why Quagmire is the way he is. A later episode, "Tiegs for Two" got more in-depth with this.
This is revealed to be part of Avatar Kuruk's Back Story on Avatar The Last Airbender. Unfortunately, the spirits (well, at least one particularly creepy one) decided he changed his ways just a little too late. Tragedy ensues.
A oneshot character in Pucca is rich, famous, handsome, and has all the Sooga ladies falling for him. He goes after the title character, who is already obsessively in love with Garu. As it always does for anyone getting in Pucca's way of Garu, it does not end well for the ladykiller.
Brock Samson from The Venture Bros. has a freakish ability to bed anyone who comes near him, but "the only woman he ever loved" was Molotov Cocktease, a badass Russian assassin who wears a chastity belt. He freely has sex with other women in spite of Molotov though, since even though he loves her, they can't enter into a relationship together. They have a history of personal vendettas which always leads to them both trying to kill one another. The fact she never puts out also might have something to do with it.
Alejandro from Total Drama World Tour. He flirted with almost all the female contestants during the third season but ended up falling for Heather.
Real Life case: Warren Beatty, aka "Warren Beauty" and his wife Annette Bening, who managed to do what women like Julie Christie, Diane Keaton, Carly Simon and Madonna could not.
Gene Simmons from KISS had a reputation of having sex with thousands of women, but is deeply in love with his current companion Shannon Tweed. They even have a pretty stable family with a couple of kids, and finally tied the knot on October 1st, 2011.
Julio Iglesias was known as a jet set man ever since his divorce from Filipina Hot Scoop Isabel Preysler. However, he met the model Miranda Rijnsburger in The Eighties, and they've remained together (though it's only recently that they got Happily Married.)