My [23F] roommate/close friend [23F] fucked my ex [29M] this weekend, lied about it

I was dating this guy for 3 months and we broke up less than two weeks ago and my roommate/close friend knows I’ve been upset about it. This weekend my roommate told me that she had a date for brunch with a guy from tinder, and I hung out with her while she got ready.

That night she never came home, or answered my calls/texts checking in to see if she was ok. She came home this morning around the same time she’d left the day before, and talked a little bit about the date. A few hours later, she woke me up and confessed that she had been on a date with my ex. (They hadn't met on tinder, she had lied to me and had just given him her number). At first she didn’t say that they had sex, but when I asked she said they did. Her excuses made no sense.

I’m hurt and upset. My roommate and I have been friends for four years and started living with each other in May, and she considers me to be her best friend.

What do I do? I'm specifically asking for advice on what to do about the living situation. I don't think i'm going to be able to forgive her, but we have a long time left on our lease. Do i ask her to move? How do I approach this?

TL;DR My roommate and close friend of four years fucked my ex this weekend, but initially lied about it. My ex and I broke up two weeks ago, and I am feeling really hurt. I don't know what to do about the fact that we live together, seeking advice.