Right, and if it was something that only happened once in a while, it wouldn't be a big deal. It just feels like it happens a lot in fiction. Thinking on it more, I guess it actually isn't that common in Marvel's comics, but in general, in fiction, if there's a gay supporting character in a story, they're either going to be effectively neuter, or they're going to be in love with the protagonist.
Admittedly, I think the main place I've noticed it is actually webcomics. It's happened in almost every webcomic I've read. So maybe that's just coloured my perception of how common it is in fiction.