Just what exactly is sexual misconduct in the Buddhist faith? Is it okay to be gay? Is it okay to have threesomes? What do the scriptures say about anal sex, contraception, and BDSM?
That's a good question, equanimity!
The way I've heard it explained by modern (also Western) spiritual leaders/Buddhist authors is that sexual misconduct is when your actions may be harmful to yourself or someone else. So, is it okay to be gay? Of course it is. A person can't help who they're attracted to, and in the event that someone is "hurt" by your sexuality (say, in the case of a very traditional parent) it wouldn't be you hurting them. Rather, their understanding of societal norms and outlook on sexual morality is in direct conflict with reality. Their delusion harms them, and you're unfortunately caught up in all that harmful delusion.
Are threesomes okay? As long as everyone involved is adult enough not to get hurt, and everyone's consenting. Might be best to avoid in many situation because of the possibility of jealousy and such, but if you can make it work then more power to you!
Anal sex? Well, I have no idea what the writings have to say about it. Probably something; there's always sex mixed up in our religions. But again, it should be fine. Same with contraception. Religion needs to adapt to modern life, hopefully without losing sight of its initial vision. Buddhism is attractive partly because it does just that.
Now BDSM is a very interesting piece to this topic. The general rule is that if no one gets hurt everything is just peachy, right? Well BDSM kind of hurts by nature. Does that make it wrong? I'd say no, but there are definitely exceptions. If you find the light pain play pleasurable and hot then that would probably be totally okay. Even the more hardcore stuff. Where I see it potentially becoming an actual problem is when it crosses over into the realm of unhealthy psychological experience. If your partner hurts you and you don't like it but don't want to upset them, you might be doing yourself some harm. If you're into being humiliated and used this could pose a problem, and your self-esteem may suffer. Each case is different and this stuff gets pretty complicated, but you should know if you're being hurt or if you're hurting someone else. Unless you're really well steeped in delusion, these things are generally pretty clear.
Use your head. Make good decisions.