Bertie: What happened to Daphne?
Bertie: The one who came after Honoria?
Bingo: Passing fancy, Bertie, the folly of one's youth!
Bertie: It was only a week and a half ago.
This character is a hopeless romantic. He's madly, passionately, fatally devoted to the girl he loves. It's just that the girl he loves seems to change from week to week. When one girl rejects him (which she usually does), he is heartbroken at first, but he soon finds a new love interest, and forgets all about the old one.
Unlike The Casanova, who strings many women along at the same time without caring about any of them, the Serial Romeo genuinely believes that each successive love is "The One", and that without her, life is not worth living. Expect this character to be completely blind to the implications of having a new "True Love" every week. If called out on his fickleness, expect him to insist that his current love interest is the only person he has ever really loved, and to dismiss her predecessors as mere youthful infatuations. Expect much eye-rolling from his friends.
Note: Although this trope usually applies to men, feel free to put female examples here as well.
- Demon Slayer: Kimetsu no Yaiba has Zenitsu immediately forgeting about the previous woman he desperately asked to marry him upon finding a new target; the only one he hasnt let go is Nezuko, partially because he might liker her more than his usual crushes on first sight and that Nezuko is a nice demon girl in a state of mind where she really cant decide or understand complex things yet, she is just nice enough not to repudiate Zenitsu on sight.
- Nana "Hachi" Komatsu from Nana was hopelessly in love with every boy she met on a serial basis, especially at the beginning of the manga.
- The Pokémon anime has Brock. But it's not (usually) because he gets rejected, but he keeps being stopped and pulled away by Misty (pulling by the ear), Max (after getting it from the former), May (on one occasion), his Bonsly (only a few times with Double-Edge), or his Croagunk (with a Poison Jab, no less).
- In later arcs, Ash's Oshawott and Clemont's Chespin take the role.
- Sailor Moon has all the Sailors relatively boy-crazy but Makoto is easily the one who has definitely had the most relationships. A Running Gag when she was first introduced was to say that a random guy reminds her of one of her old boyfriends.
- In the manga, Minako tops her by a few orders of magnitude. During Codename: Sailor V Artemis kept count of Minako's 'first loves' (as she called them), and the final chapter had him sarcastically congratulate her for her 5,000th first love.
- Martina of Slayers Next falls madly in love with just about every male member of the cast she meets. The fixation on Zangulus at the end of the season lasts long enough to get her married off.
- Super Gals has Naoki, whose entire characterization consist of him falling in love with an unavailable girl, getting heartbroken when he finds out that his "soulmate" already has someone else, then falling in love with another (unavailable) girl when he tries to leave for some soul-searching. Over the course of three volumes, he's fallen in love with Ran, then Miyu, then Sayo, then Aya.
- Miles Morales has an ever-growing list of infatuations on superheroines his age: Ultimate Cassie Lang, teen Jean Grey, Ms. Marvel, Spider-Gwen, and Starling are among the most prominent.
- Ms. Marvel supporting character Zoe Zimmer is extremely unlucky in love. She has had feelings for in Nakia (who is straight), Kaylee (who is actually a killer robot), Alanna (who disappeared after the arc in which she debuted), and Marissa (who has only been mentioned in dialogue). Even Josh, the one guy she dated back when she was still in the closet, dropped out of school to become the super villain Discord.
- Sameer from the Bollywood movie Dil Chahta Hai. Unlike his friend Akash, who is The Casanova, Sameer believes that he is truly in love which each new pretty girl he meets, and is heartbroken when they reject him. His despairing parents eventually try to set him up in an arranged marriage with a girl named Pooja. Fortunately, Sameer ends up falling in love with her, too!
- Discussed in Mamma Mia! Here We Go Again, Donna guesses Bill is this sort, and sums up the distinction between this trope and The Casanova. "One who actually does fall in love every night, but always falls out of it the next morning." However, there's scant evidence that Bill is actually like this, but plenty of evidence that Donna is a female example. She seems to have genuine feelings for Sam, Bill, and Harry, despite meeting them all within a couple of weeks.
- An Abundance of Katherines: Maybe not every week, but Colin has dated more girls named Katherine than he's had years in his life.
- Claire Stanfield from Baccano! has a history of this, literally falling in love and proposing marriage to complete strangers, almost at random. He has a hard time convincing his brothers that his relationship with Chane is any different other than that she didn't immediately say no.
- The Dresden Files novel Blood Rites features Arturo, who has been married (and divorced) thrice and currently has a new beau. People who know him claims that he is capable of intense love towards whoever he's got his eye on at the moment, but has a problem when the magic dies it is notable that in a universe where The Power of Love is real, Arturo is capable of showing it towards anyone he's interested in. It is revealed at the end that for the first time, he married a plain woman. Perhaps this one will last.
- In some of the Dragonlance Novels detailing the early lives of the Heroes of the Lance, Caramon is described this way. His brother makes some snarky remarks about his tendency to be in love with a new girl every week, though eventually he settles down with his true love Tika.
- Gösta Berling spends most of Gösta Berling's Saga falling desperately in love with one woman after another, winning her love, turning her life upside down, and then moving on to do the same thing to someone else about ten days later, until he's eventually forced to grow up.
- Howl from Howl's Moving Castle pretty much defines this trope. He goes out, falls in love with a girl, spends an inordinate amount of time and effort wooing her, and then...drops her once she falls in love with him. Repeat on infinite. The first one he fails to do this to is Sophie, who turned him into a Lady Killer In Love and whom he eventually married.
- Bingo Little from P. G. Wodehouse's Jeeves and Wooster series, although he eventually gets married and settles down. Bertie himself could count as a milder example—he falls for one Girl of the Week after another, but generally ends up expressing relief when things don't work out.
- William's older brother Robert from Just William seems to have this as his primary character trait, meeting "the most beautiful girl he's ever seen in his life" an average of about once a week. The narration often gently mocks him for it.
- Sansa from A Song of Ice and Fire has shades of this. She falls quite hard for Prince Joffrey at the first hint that their parents are considering bethrothing them. She fantasizes about marrying Ser Loras both before and after Joffrey's true nature is revealed and she falls out of "love" with him, then transfers her affections wholly to Loras' brother Willas on being offered a secret marriage pact to him, without even meeting him. Seemingly the only male she DOESN'T fall in instant love with the moment a possible romantic relationship is suggested is her eventual husband, Tyrion. Not without a certain amount of justification.
- Stray: While Pufftail was a Casanova during his youth, his brother Bootsie was one of these. He was a hopeless romantic but it's also mentioned that few mollies in their neighborhood didn't know either Pufftail or Bootsie.
- The Stormlight Archive: Adolin is this in spades. Frequently lampshaded by his brother, and several other characters. In the second book he's fine with the prospect of an Arranged Marriage to a woman from an insignificant house he's never met partially because by this point he's offended literally every other eligible woman, and the idea of letting someone else make the arrangements sounds good. Oddly enough, the Arranged Marriage seems likely to become a Perfectly Arranged Marriage, as he and the girl in question fit together quite well. There's a bit of a Running Gag throughout the second book where Adolin will be in the same scene with a random woman and she'll glare at him. At one point, the woman teaching Kaladin's men how to care for their horses starts throwing stones at Adolin without missing a beat. In the third book, Shallan mentions she tried avoiding Adolin's exes, but quickly had to give it up as impossible.
Shallan: They were like soldiers on the battlefield. They were just sort of everywhere.
- In These Words Are True and Faithful, a running joke among Ernie's friends is that Ernie declares every new object of his infatuation as the one with whom he is meant to be.
- Tortall Universe: Very much the case with Neal from the Protector of the Small quartet, although he eventually gets over it and gets married. Before that happens, though, he gets lovelorn crushes on women like Queen Thayet and Lady Uline, and is at one point beaten with loaves of bread by his friends when he starts going on about one of his crushes in the middle of supper.
- In Will Grayson, Will Grayson Tiny Cooper is constantly swooning after and being heart-broken over guy after guy (after guy after guy). Apart from his gay-ness and large-ness, this is practically his defining feature.
- 7 Yüz: According to Nil, Metin of "Biyolojik Saat" is one. He easily finds new women to date after a breakup, but slowly realizes that not everyone he attracts is a good match once he begins looking for a quality lifelong relationship.
- Phoebe from Charmed starts out as one but eventually evolves into a Deconstruction. The endless stream of failed relationships leaves her emotionally damaged and terrified of heartbreak again. After she gets a vision of having a baby in the future, she misuses her powers to see if her relationships will go anywhere on the first date. The final season Reconstructs it when she decides to get a sperm donor and she then realises that she doesn't just want a baby, she does want love as well and a Cupid gets sent to help her overcome her relationship issues.
- Izzie from Grey's Anatomy is a female version. Her "true loves" include her patient Denny Duquette, George, and Alex.
- Ted Mosby from How I Met Your Mother realizes that the odds of the next girl he's interested in being The One are pretty dismal. It doesn't stop him from trying.
- Lampshaded in a later episode when Lily complains about all these random girls showing up in their group photos.
- Bingo Little from Jeeves and Wooster, in the show's first three episodes alone, is "in love" with four different girls!
- S Club 7 had one as a landlady in LA 7 by the name of Joannie. She has pictures of all her old boyfriends in her living room and her first episode has her describing many of the relationships in great detail to a concussed Bradley. Poor Paul actually has to pretend to be one of her boyfriends in a later episode.
- Dylan in Lovesick. Luke says he "falls in love twice a week". His ongoing love for Evie in the present is different, but in the many flashbacks he definitely fits this trope.
- Dobie from The Many Loves of Dobie Gillis. The series was named that for good reason, as just about every week Dobie was chasing a new girl who he thought was the love of his life.
- Davy from The Monkees tended to fall in love with a different woman in almost every episode. There were even a couple of episodes where he'd fall in love with two different women, one at the beginning and another by the end.
- Every woman Mark from Peep Show meets might be The One. Even Jez has streaks of this, though he's just as likely to use a women for sex with plans to dump her ASAP.
- The music video for "Cupid's Chokehold" by Gym Class Heroes implies this about the protagonist. With each verse describing how great his girlfriend is (one lyric is "I know I'm young but if I had to choose her or the sun/I'd be one nocturnal son of a gun"), a different woman is shown.
- "Romeo and Juliet" by Hobo Johnson discusses the trope namer's tendency to fall in love easily both by using it as a metaphor for Hobo's own string of failed relationships, and by suggesting that if the two characters survived the play, they would have gotten divorced.
- The backstory of Prozzak, as deduced from their songs, is a long series of romantic misadventures, with Simon in particular constantly thinking he's found true love only to immediately lose it.
- Swashbuckling adventure game 7th Sea has the Hubris "Starcrossed" which means the game master can spend one drama die to have your character fall in love with another beautiful NPC whenever he wants.
- The Trope Namer is Romeo Montague from Romeo and Juliet. At the beginning of the play he is desperately in love with a girl named Rosaline, who has rejected him. Soon after, he meets Juliet, and promptly dismisses Rosaline as a passing infatuation. Though this only happens once in the story that we know about, goodness only knows how many more times he would have gone through this had Juliet also rejected him.
Did my heart love till now? Forswear it, sight;
For I ne'er saw true beauty till this night!
- Larry Butz from the Ace Attorney series is constantly either trying to get together with a woman with whom he's fallen madly in love, or just been dumped. We rarely see him actually in a relationship. This is a big part of his character, though: He also has a different job every time we see him.
- Jenon of Blaze Union, at least from the way Garlot immediately groans and goes "well, here we go again" when he falls for Medoute.
- Subaki's daughter Caeldori from Fire Emblem Fates is said to be "the one who falls in love the easiest in the army", and in her own words, after having her first Love Confession rejected, she's crushed on guys who were unavaliable to her for one reason or another. Naturally, when she actually falls in love in-story, she drops this attitude.
- Lowell from The Last Story. He actually became this way from seeing every woman he fell in love with die violently, thus resolving to never have a serious relationship ever again.
- A series of sidequests in Shin Megami Tensei: Strange Journey involves the player character delivering love messages for a crewman named Anthony, who falls in love with a succession of female demons. And the first few times, the music cuts out when Anthony confesses this fact. Eventually, Anthony grows up a little, and the last of these quests has him ask you to look up a goddess of love for advice on how to talk to human girls.
- The Questport Chronicles: Although the Lord of Angels and Demons is treated as The Casanova in-universe, he's actually more this trope, especially with regards to the Secret Keeper and the Queen of Rogues and Robbers.
- Rosethorn, of the Whateley Universe, whose first name really is Romeo. He's strikingly handsome (or, as he is more often described, beautiful), and has mutant powers. He tends to find Miss Right, make her over, improve her self-esteem, etc., until she dumps him. She always dumps him. Either she hates being the dumpy one in the relationship, or she becomes 'pretty' enough for other guys to see her as desirable, or the whole 'my mother is a dangerous supervillain' thing comes up and torpedoes the relationship, or...
- Sonichu's Christian Weston Chandler gives this impression quite a bit. It's not intentional, though, being an Author Avatar, many of his comic girlfriends are based on Chris's real-life girlfriends, including Meg, Blamca, Julie, and Ivy. Given that many of Chris's real-life girlfriends were at best mild acquaintances and at worst Internet trolls, this leads to the comic Chris pledging his eternal love to a girl who's never appeared before as soon as real-life Chris gets a girlfriend, then the girl being swiftly written out the second real-life Chris loses the relationship.
- Gravity Falls has Mabel as a female example of this trope. However, "Society of the Blind Eye" shows she's not taking her failed attempts at a summer romance (like Norman, who "turned out to be gnomes", Gideon, who was a Stalker with a Crush who threatened her family, and Gabe, who made out with his own puppets) as well as she lets on.