I'm going to make my girlfriend choose me or her housemate
Why are you forcing her to choose like that?
I'm sick of her housemate, she is hurting my relationship with my girlfriend.
I'm sorry you're having issues with her roommate.  However, you don't get to decide who your girlfriend talks to or lives with.  It's her call and you're being way too controlling about this.
I'm going to make her choose anyway. If she wants me then she will pick me. If she wants her roommate than she can continue to live with her.
That is an unfair thing for you to do. Giving people ultimatums usually turn out for the worse. You shouldn't force your partner to choose between you and someone else but it might not end up the way you want.