The Hour before Morning (science fiction/science fantasy) is about 3 people in a prison cell together, 2 men and 1 woman. It starts out with the men and the woman comes in later. The men are not sexually/romantically involved in an explicit way, but they kind of are in a metaphorical way. They have a telepathic bond that produces uncomfortable mental intimacy and sometimes verges on rape metaphors. My friend, who is very into slash and "slashy" texts, really liked this story when it was just about the 2 guys but was disappointed when the woman came in and one of the guys fell for her. She felt like, "There's the old heteronormative context again." I've thought about this a lot though, and I think the introduction of the woman is actually necessary to the development of the relationship between the men. Without her, they'd just go on being sort of close but sort of uncomfortable with each other. But with her, the tension over their telepathic bond gets heightened because the one doesn't like the other "spying" on his feelings for her.
I feel like--in a "genre" sense--the whole issue is a bit thorny. I don't want the female character to be a conventional love interest or just a prop for the men's relationship. I am also a little uncomfortable with the idea that the "woman" necessarily sabotages a nice story about 2 men. On the other hand, I don't want to sabotage an interesting, unusual dynamic between two men by introducing a woman who shifts the focus off that relationship and onto conventional "romance." I'm babbling, but your thoughts are welcome.