You are roommates? Is that like college roommates? Or do you share an apartment or something? How old are you?
In my experience, it doesn’t really make sense to take relationships as seriously when you are in your twenties. That’s just my experience. I hung with a crowd where just about everybody slept with everybody else at one point or another. We didn’t know who we were or where we wanted to be, so we were just trying things out. Some of the women had lesbian relationships, and even called themselves lesbians, and later on they married guys.
You, yourself, say you don’t consider yourself a lesbian. So what is this affair, then? Are you just trying something out? Or is this something you want to be serious and forever, maybe? If you’re not really into girls, then this doesn’t seem like a long term relationship.
You say that she’s kind of trapped. She doesn’t love him, but she feels marriage is somehow inevitable. Why can’t she break up with him? Since when did women become slaves to men? I thought women were emancipated long ago.
Well, for whatever reason, she can’t handle her own life. So maybe she’s using you as a way to get the strength to break up with him. Maybe she hopes he’ll catch you some time. Or maybe she’s recruiting you for a threesome.
Whatever. I think the best thing you can do is to help her sort herself out. I don’t think you have any business “demanding” anything from her. That’s pretty selfish. If you love her, then you should want to put her interests before yours.
Let her break it off. Then you guys can do what you want. If she can’t break it off, you should ask yourself if this is really a person you want to be with?
The other thing to ask yourself is whether this is more about the drama than about love. Nothing seems very permanent here, and so maybe you are making too much of it. I’d be really careful, though. You stick your nose in there in any way besides being a friend, and it might get nipped off.