I'm going back on an agreement to let my friend keep living with me
Why are you changing your mind?
She was a sexual partner for me and I got tired of having sex with her.
I think that maybe you should just talk to them instead. You already came to an agreement, it seems wrong to go back on it now.
It's not just because of the bad sex.  She's just someone I don't like anymore.
It is understandable that you might not want to live with someone you don't like but if you have a written agreement, you might not have a choice. It would be good to at least give her sometime to find somewhere else to live.