Speaking from the male perspective only, before DAO, it seemed like almost every Bioware fantasy romance option (can't speak for games I haven't played) likely had a heartbreak ending. Weren't most of the BG2 female choices flawed somehow?
Viconia- rewarding story, as the Hero could move her away from evil, yet in the epilogue, she ends up being murdered by assassins.
Aerie- It was easier to feel sorry for her, than see her as a romance option. Very whiney.
Jaheira-Nothing like trying to romance a bitter, recent widow, who used to babysit you. Still, was a well written character...but definitely heartbreak involved.
NwN1- From what I recall, only one option, Aribeth. And if that was not a case of heartbreak, I do not know what is. No matter what the Savior of Neverwinter City did, to save the sorry butts of Lord Nasher and all his pathetic subjects, his girlfriend was going to be executed, without even a chance to protest. They tried to make up for it, in the third installment, by letting you romance her ghost (golf clap).
DAO: Morrigan was probably the best written romance, imo, of any I have played. Even when she ran away, you had the option to chase after her. And so, it was satisfying, even before the Witch Hunt DLC. Leliana was good, too. Just did not seem to have the complexities to make it as memorable.
DA2: Merrill barely felt like a romance, not sure why. Then with Isabella, it felt like she was playing you the whole time. I believe the OP commented on how Alistair might cheat on you? Isabella made you feel like you had to take a number and wait in line.
DLI: Cassandra was surprisingly decent, at least up to the point where the big love scene was. After that....apparently the writers had better things to do.
Cannot comment much on Josephine. She seemed to be a fairly well written character, and the flirts were fun, before I made the decision to romance Cassandra. Not interested enough to replay the game yet, to see how the Josephine romance turns out. I have the feeling Cassandra would have been the better of the two choices.
So, while I can understand where you are coming from OP, and would be happy to see you get your wish, it hasn't exactly been all shiny on the other side of the spectrum.
BG2: Male protagonists get 3 romances, female protagonists get 1. That's right: One. Anomen. How well did you like Anomen? (I liked him just fine, but a lot of people did not.)
NWN: Don't complain about male protagonists only getting one romance, because that's how many female protagonists got, too, and Valen's got his own issues.
DAO: Wah. You had to wait for the DLC to reunite with Morrigan. At least all of the female LIs are equipped with dragonbone plot armor. Not only are both of the male LIs killable, they both visit unhappiness on the PC. Zevran leaves and if Alistair is to survive at all, you have to force him to cheat on you with another woman. And if you aren't a human noble, he dumps you. Think you found a happy ending in keeping him a Warden? Play DAI. Years later, BioWare ensures that even those who managed to somehow find the one happy ending for Alistair get screwed. Thanks. Regarding Zevran, you get him late in the game, it's easy to kill him without even realizing he's a LI (leaving you with precisely one choice, who will either dump you, die, or cheat on you... or some combination of the above). Zevran may betray the PC, and he is pretty much never referenced again even if he doesn't. Compare that to the female LIs, both of whom are not only immortal, but become icons. They wrote two character based DLCs, one for each female LI while the males were ignored. One of those DLCs was written specifically to give Morrigan romancers their happy ending. That hardly seems fair. So by my lights, the verdict is: Male LIs don't get happy endings, female LIs do.
DA2: Again, the males are killable. One of the females is. Merrill is a romance regardless of whether you liked it or not, and Isabela is no worse than Zevran. Seriously. Not sure *anybody* got a happy ending here, but it seems as if Merrill and Isabela offered more hope of it.
DAI: A bit more of a mixed bag. I've only played Blackwall's romance and Dorian's, but I'm already noticing a trend that the tradition of making people who prefer men to women suffer continues. On the other hand, I understand that Cullen's romance and IB's have happy ending potential. I haven't played Cassandra's romance, Josephine's, or Sera's, so I can't really say if they do.
So yeah, if I could ask for one thing for some future male LI, it would be a happy ending for a plot-significant male LI. One who survives the closing credits.
On another topic, is it really necessary to have the "betrayer" always be male? Zevran. Anders. Blackwall. I love them all (and Anders and Blackwall are my favorite romances for their respective games), but it's getting old. If you're going to sling mud, it's OK if some of it hits the women. Yeah, I know, women are vilified often enough in society and we don't really need to perpetuate that, but in BioWare games, it seems as if the worst crime they ever commit is having a sexual past (Isabela gets a *lot* of totally unnecessary and really rude hate, but Zevran and Iron Bull are at least as promiscuous or even more so and it's ignored). It's OK to write a woman who uses something other than sex to get what she wants.