Barely even happens, sadly - we're at that awkward point when everyone tries to do it, but nobody really knows how to and it ends up feeling forced.
The real problem is that we're just not used to it, so each time a character ends up being gay we question the point of it instead of just taking it as-is. And, well, it will feel forced for a while because in all honesty, a character's sexual orientation is something that would usually barely matter in the context of the story.
If it doesn't matter and is still explored, it feels forced because in the end who gives a shit if it has nothing to do with the plot. If it's made to matter and centers the context of the story around it, it feels forced because you get that sore feeling of being force-fed muh progressive representashun.
A good example of it being done right, if in a somewhat old-fashioned way, is one of the early 90's story arcs in The Sandman (A Game of You, i believe) - there's a lesbian couple, it's clearly pointed out that they're lesbians and it's made relevant to the context, but the story doesn't really make that big a deal out of it.