What do I do with my “cheating” friends with benefits?

I 18m am in an open relationship. I 18m found a good friend from highschool 18f and we hit it off. 18f was previously in a relationship in highschool but ended things a few months before graduation. 18f and I have been on and off going on trips and hanging out a lot and doing the dirty. We have been talking/dating without the label for over 4 months now. Before I get into the story 18f is a complete 10/10 hidden gem in highschool and one of the most popular girls. I 18m was not very popular and rate myself a 7/10 if not lower. 18f promised me that if she was to get with anyone else she would tell me before hand, she knows that I am in an open relationship and was fine with it. On the other hand I wanted to know if she was getting with other men during my time with her. I was out with friends and 18f when I noticed a hickey on 18fs neck. I haven’t seen her in days. IT WASNT ME! I decided to trap my anger and worry about it once I compiled my thoughts. As my friend let’s call him “ken” was taking 18f and i home after hanging out I decided to confront her. As ken was talking about something funny he had previously said I interrupted and said “you know what else is funny? The hickeys on your neck that weren’t from me.” 18f was silent. Ken turns around and shines light and says omg is that true? And see said marks. As 18f is completely silent ken and I talk about random things as I’m holding back my anger and sadness as we drive to 18fs house. We finally drop her off and 18f says “can I at least please take you home” I don’t respond and stare straight holding back all my anger. 18 f says “please, please, please” begging and begging. I tell her she’s horrible and I’m lucky I don’t go crazy. She now is calling me and texting me and she wants to start over and wants my trust back and how she feels bad and how she was going to tell me. What do I do? 1. Forgive and forget. 2. Never talk to her again like I told her. 3 suggestions? I really really like her think she is hot and is very nice to me. We never fought ever and things were always smooth until now. Is this a deal breaker? Help me out.