In Homestuck, due to the complicated social dynamics and age of the protagonists, this trope gets used a lot.
In particular, with Karkat Vantas, who despite being adept at helping other people sort out their romantic issues, is constantly tortured by his inability to sort out his own, in particular, with Terezi, his love interest. Being a self-loathing Jerkass Woobie doesn't help this.
Eridan Ampora also invokes this, as he desperately hits on everyone but ends up with nothing to show for it, usually to comedic effect. This is justified because he is a douchebag, but later becomes a lot less funny when it becomes a factor in him murdering two of his friends.
Nepeta Leijon also qualifies. She wants nothing more than for Karkat to just notice her, but she doesn't think that anything will ever happen. And then she gets horrifyingly butchered by an Ax-Crazy Gamzee.
Davesprite and Jade breaking up is an interesting example of this; Jade initially seems largely unaffected by the whole thing despite the fact that Davesprite's the one who broke up with her. It's Davesprite himself and, oddly enough, John who seem to be upset about the whole thing (Davesprite, being Dave, isn't exactly emotional about it but doesn't appear to be all too happy about it either; with John it's implied to be a Big Brother Instinct scenario). When Jade is under mind control, her confrontation with Dave has her vent some of her feelings about the relationship, shouting that he broke her heart.
Jack: The American Ghost: Jack and Go-Eun inadvertently cause each other a lot of pain while trying to help and save the other. Ouch.
The Beast is crazily obsessed with Beauty and rages, insane with jealousy, when she's late returning.
Prince Ricardo, being Minor Flaw, Major Breakup embodied, goes around breaking hearts as quickly as he can rescue princesses — and is none too happy himself.
Claire and King Gareth appear to have been Happily Married, but he went to war. Now they are separated; Claire won't explain what happened to her child, and refuses to meet him because she feels too guilty; and Gareth signed a peace treaty because he was too heartbroken over the news of his wife.
He gets off easy compared to Oasis, who has died multiple times because of her unrequited love for Torg.
While Lia and Fiona, from YU+ME: dream , don't have any easy time at first, this is nothing compared to when the major Drama Bomb hits. This seems to be intentional, as the author/artist explains here.
Zoophobia: Damian's obsession with Kayla always leads to this.
.