Okay so I'm kind of having a relationship issue, but I'm not in a relationship.

I was dating this guy, and about five months in we started having issues. He got mad at me for talking to my best friend/ex at Church (never outside of it unless he had a guitar question). My (now ex) boyfriend started helping this girl at his school (he lived a town over) with her relationship issues, and they quickly formed a friendship. Great and everything, but he didn't tell me aboutit until he started talking about her like it was casual conversation and I was like "whose [insert name]?" After that they started getting super close, closer than he and I were. We started compesnating for the lack of trust with sexual activities (not sex), and decided to take a break. After a few days he broke up with me, saying his parents made him. A couple days after that, he made his best friend tell me the truth - he had left me for the girl he was "just friends" with. We stopped talking, but a while later he texted me and we wanted to be friends, until he openly admitted to cheating on me, then got mad when I became depressed, blaming myself because I knew deep down he had. We stopped talking again. Now we're talking again, and he says he loves me and misses me, and he knows he did everything absolutely wrong. We've both done stupid stuff because of depression. But if I ever did get back with him in the future, I don't know if I could deal with the other girl still being in his life (theyre best friends). He always posts her on his social media, and she's so dann pretty I get super depressed and self conscious when I see her. As if my insecurities werent big enough. I don't know what to do?