I'm thinking of my roommate making out with this guy while I'm in the room.
Why are you thinking about this?
She knows this bothers me, but she does it anyway.
I understand, it's maddening when your roommate isn't respecting your privacy. You should tell her to stop doing that.
I don't know how, I don't feel like I can talk to her about it.
It can be quite frustrating when you roommate does things they know bother you but don't care. You need to put your foot down and tell her to stop or either you or her will move out.