I'm not going to allow my roommate's girlfriend to come over anymore.
What is your reason for not allowing it/
Because they make too much noise when she's here.
Although it might bother you when she comes over it's not fair to ask your roommate to curtail their love life. Don't tell your roommate when they can have other people over.
I'm sick of her relationship with my roommate and they are always making out. It might turn into love making and I'm uncomfortable hearing them.
I am sure it can be annoying to hear their love making, however just try to allow your roommate to have fun with their girlfriend. It is your roommate's home as well, so having a conversation with them about it may be the best way to deal with the situation.