As a writer I've written about all sorts of sexual encounters, and that includes several same-sex ones. I have a couple of M/M stories published at the moment, and you can bet your buns there'll be one or two F/F ones showing up at some point over the next several months. As you can imagine, I've had more than a couple of people ask me whether I'm bisexual after having read some of my work. Spoiler alert: I'm not. Not even a little. I consider myself very firmly heterosexual, I just happen to find same-sex encounters incredibly hot.
That probably sounds weird to some of you, but it's all about the difference between sexual attraction and romantic attraction. Unfortunately society doesn't often make that distinction, and sexuality gets lumped into "straight", "gay", "bi" without much consideration for its different dimensions.
I'll tentatively say that I think most adults who have a vested interest in sex beyond the norm get to grips with this concept pretty quickly. They're beyond the adolescent worries of "if I fantasise about a member of the same (or opposite) sex does that make me gay (or straight)?", and the more you get into exploring different sexual kinks the more open minded you tend to get about how and why different things turn people on.
In the two M/M stories I've published so far I actually make a point of establishing that the male leads are both heterosexual, to make the distinction between sexual and romantic attraction. They both have girlfriends, they're both in stable heterosexual relationships, but gay sex is still something that turns them on. I do this because it "fetishises" same-sex encounters for me. It makes them more accessible and naughty to a heterosexual audience. I feel like I'm going to have to put a disclaimer here that I don't intend to portray homosexuality as a fetish in and of itself - only as a straight person's fetish. I'm sure there'll be romantic same-sex encounters in my writing in the future. :)
I do like to explore the emotional subtext of sex whenever I can, and my hope is that, on top of being super-steamy reads, some of my stories can engage people in thinking about sexuality in different ways from time to time.
You don't have to be gay or lesbian to enjoy gay or lesbian sex. Sex is hot, no matter who it's with.