Fortune has me well in hand, armies 'wait my command My gold lies in a foreign land buried deep beneath the sand The angels guide my ev'ry tread, my enemies are sick or dead But all the victories I've led haven't brought you to my bed
Dream from The Sandman is the God of his realm, but when he fell in love with a mortal woman, their forbidden love destroyed her city. Fearing worse things, the girl denied him (thrice?) until he sent her to Hell. As you do.
In a comic where they meet for the first or the nearly first time, Captain AmericaevaluatesSpider-Man and concludes that the kid is serious about what he's doing. He didn't sign up to impress the girls. Spidey tells him that the girls he knows would need way more to be impressed.
In Disney's Aladdin, making someone fall in love is one of the few things the Genie can't do.
In the original Bedazzled (1967), the hero's deal with the devil spectacularly fails to get him the girl of his dreams at least five times. It's only after he gets out of the deal that he can go back to being an innocent short-order cook and win her himself. In The Remake of 2000, he ends up with a different girl than the one he was trying to get with his wishes. note Since both girls are played by the same actress, presumably we're intended to believe that on some level he did actually get the girl of his dreams. Well, that, and that the second girl reveals (in the mere minutes she's seen) that her tastes are almost identical to his, as well as her quirky sense of humor.
Bruce Almighty — Bruce is given the powers of God himself, and he still can't use them to get the girl. Worse, he already has the girl but his powers are no help in keeping her. In part, the problem is his powers can't affect free will, but c'mon, that's not hard to get around.
The movie Other Peoples Money ended on a bittersweet note, as Larry had to live with the fact that being the best at what he does, and staying true to his unorthodox but sincere sense of ethics, had brought him resounding success as always, but at the same time driven away his love interest. It's an unusual and thoughtful way to leave off. It should be noted, however that the last lines of the film imply that Larry and Kate will end up together, and in the original play, it is explicit that they eventually marry and have children.
What Women Want — Telepathy that only works on females. Something of an aversion: it really does help him in as much as it reveals enough of her inner-self that he falls for her, but then he feels too guilty to abuse his power in order to win her heart or bed her (which backfired when he did that with the coffee-shop girl who subsequently became obsessed with him because the telepathy made him so damn good in bed).
The plot of the short film Validation, in which the hero tries everything to get through to his love interest, to no avail. When he finally gives up, things take an unexpected turn...
Robert Baratheon of A Song of Ice and Fire went to war against the Mad King to rescue his beloved, Lyanna Stark. When the dust finally settled, Robert has become king and commanded all of the Seven Kingdoms, but Lyanna had died regardless. He made it no secret that he was bitter about a crown he never wanted and a girl he had lost.
Also, in a more twisted example, resident Chessmaster Petyr Baelish rose from a poor lord laughed at by everyone to an incredibly influential politician with all the wealth and respect he could want, but not the girl he was interested in when he was fifteen who's now dead, although he's acquired a Replacement Goldfish in the form of her (barely) teenage daughter Sansa.
Angel: But she's not finished baking yet! I gotta wait till she's done baking! You know, till she finds herself, 'cause that's the drill, fine, I'm waitin' patiently and meanwhile, THE IMMORTAL'S EATING COOKIE DOUGH!
Andrew: Uhhh, Spike, is Angel crying?
Spike: No! (in the same defiant tone) Not yet!
He was slow on the draw with Cordelia, as well. She packed off and left with the Groolalugg, another superhuman warrior who isn't allergic to sunlight.
In Merlin, Lancelot eventually realizes his life-long dream of becoming a knight of Camelot, only to regret his decision to leave Guinevere at a point in which there was nothing standing in the way of a relationship with her - nothing except the realization that Arthur was in love with her as well.
The theme of Ne-Yo's 2010 album Libra Scale is that after having saved the city, he's awarded fame, money and power but at the cost of never being able to fall in love. Not a problem until he actually falls in love with somebody.
This is Strahd von Zarovich's big Dark-Powers-dispensed curse in Ravenloft, in that he is an absurdly powerful ruler in his own domain, but the woman he did all those horrible acts that got him stuck there in the first place to attain is dead. And to further twist the knife, she reincarnates once every generation, but Strahd is cursed to always end up leading her to her death and making her loathe him.
Fate/Stay Night — In a villainous variation of this trope, Gilgamesh was quite literally said to have owned everything there was to own, but still pursued Saber madly in his own sicktwisted fashion.
Oh, and no he does not learn to use his power to help people. He, instead, tries to kill Saber's love interest (Shirou, the main character), and corrupt Saber with All The Evils Of The World. Saber ends his madness by cutting him in half with an Excaliburst.
In an interesting example in Plants vs. Zombies, if you read the biography on the Gargantuar, you see that he shakes the earth when he walks, all other zombies yearn to be him, and other impressive stuff. But he still can't get a girlfriend.
This is one of the twists to the ending of Conkers Bad Fur Day. And he doesn't even want the crown.
In Spellcasting 101, Ernie manages to score with several women during his adventures. Ultimately, the one he does not manage to impress is his true love.
Doctor Horrible's Sing-Along Blog. Minus the helping people, he's the Ineffectual Sympathetic Villain. Dr. Horrible (or Billy) wants to join the Evil League of Evil to gain power from what he sees as a corrupt society, make the world a better place, and win Penny's heart by doing so. However, to earn his way into the League he has to kill someone and tragically, Penny winds up dead. Billy finally gets to join, but says he doesn't "feel a thing" anymore, and all the power and respect he's fought for is hollow.
In a somewhat similar case, this is subverted in Soon I Will Be Invincible, insofar as getting the girl is the only thing Dr. Impossible does manage to succeed at... although he doesn't realize it.
The Fairly Oddparents: Magic can never interfere with true love, so Timmy still hadn't gotten Trixie to fall for him.
Amusingly inverted in the episode featuring Norm the Magic Genie, whose wishes can affect love, but Timmy words the wish just wrong and every other "Timothy Turner" in the world gets Trixie's love except him.
Actually, Timmy was about to get his turn when, in order to rescue his Fairy Godparents, he made Norm undo all his wishes.