I'm going to ban my roommate's girlfriend from our dorm
Why would you want to ban her?
They have really loud sex, its disturbing.
It is ok to find other people annoying. You should talk about it and let them know so you can have plans and keep harmony in your dorm without fighting.  Perhaps you could arrange for times when the dorm will be empty?
But there is that saying "don't fuck with me or I'll fuck with you!" That is what I'm feeling right now. I am tired too and not getting much sleep from their noise.
I have heard people saying things like that, but only in the context of violent threats.  I really don't think that's what you want to be saying to your roommate.  Just tell him that it's inappropriate to have loud sex in a shared residence, and try to work out a compromise.