When I went to visit my long distance boyfriend for two weeks (this is not the first visit) I found messages on his phone between him and another girl indicating they had slept together. I also found flirty messages with other girls but nothing that was extreme, he seemed to be disinterested but he never outright rejected them. There was also his friend A who I saw messages from and realized he had slept with her 6 months to a year before we met and she ended up having feelings for him. Throughout our entire relationship she was always asking to sleep over (platonically) but he always denied. It shocked me I didn't know this.
I confronted him and he admitted he slept with one girl from his work (he told me in the past he wasn't interested in and rejected her advances) and the rest were old girls from before we met that he just felt too guilty to cut off but never did anything or cheated with them.
I was devastated. I asked him why and he said this was before we had ever met in person and he had never felt this way for someone online and didn't know if we would actually ever become an in person couple but now that we have he knows I'm the one and wants to have a future with me and can't see his life without me. He told me he was going to tell me but was waiting for the right time.
It was obviously a one time thing, any time she asked about sex again in the texts and flirted with him again he made some sort of excuse (bed too noisy, uncomfortable etc.) and I looked through the rest of his phone and he didn't sleep with anyone else and all the girls who were interested in him he had stopped talking to for a while. He also explained his friend A wasn't a threat and I shouldn't worry as I can see from the texts he never wanted to be more than friends after they hooked up. (The texts do show that) We both love each other and it was obvious how guilty and sorry he was. I decided to stay with him.
This was all 1-2 weeks ago. However, now that I'm home every time he goes out I'm wondering if it's happening again. I'm always wondering if he's texting another girl or if A is coming over and I don't know (She never has before). He is in a fraternity and tonight is bid night and he says theres no girls there tonight because of covid but I can't stop worrying since I won't hear from him until tomorrow. I know I need to trust him and stop thinking of all the possibilities or I'll drive myself crazy especially since I know there's no way for me to know and he would most likely be open with me if something did happen. I just can't stop driving myself crazy over this and I'm close to crying. Any advice on how to let this go and trust him? How do I keep calm when he isn't here?
Also, please don't just tell me to break up with him. I really want to give this a shot.