Since you're separated, this usually means both shouldn't be having sex. If you're sure you don't want any part of this, you need to tell him firmly and even change the lock and don't answer when he comes. Even get a restraining order if you have too. You don't want to feel used and maybe he's having sex with other women - chance of STD's. This is your body and he needs to know you're dead serious.....not be cajoled into cooperating.