I [19F] am trying to save my relationship with my [20M] boyfriend after he cheated.

I [19F] have been going through a complicated situation with my [20M] boyfriend. We started dating in October of last year and about 2 weeks after we started dating I received a text from his ex telling me that they had been sleeping together and she sent me a bunch of proof. My boyfriend then called me and explained to me that he stupidly kept talking to her after he and I got together because he was worried about what she would do to herself if he cut her off. So I looked at everything she send but a lot of the evidence was edited dates and some of it was just downright not possible because he was with me on said dates she claimed they had seen eachother, so me and my boyfriend talked about it and we decided to just keep moving forward. The next couple of months we kept getting into a lot of arguments, I was deeply affected by what has happened, because it was a scary thing to go through especially since the time we had been dating, everything felt so perfect. I would often cry to him about how insecure I felt after that and how I felt so scared that he would start talking to her again. He really sucked at reassurance, and that made my overthinking worse. To the point where he would start getting frustrated and ask me why his efforts weren't enough. It went on like this for a while. Fast forward to a random Saturday night, we were having another argument, but before that we had agreed to go out the following day. So on Sunday I was just waiting for his text so that I could start getting ready to go out with him. I heard nothing from him all day, and then he showed up at my house later that night like he didn't just ghost me the whole day. Another argument pursued. He told me how he had wanted space and that he didn't wanna just tell me that cause he knew I would get upset. And I started crying telling him that he can't do stuff like that because he knows how bad my overthinking can get. He didn't even respond to that, and I was just sitting there crying, I just kept thinking about how much we had been arguing and how his efforts seemed to have been fading. I sat there crying for an hour, he did not hug me or comfort me or say anything. We ended up making up in the end. The next day Idk what made me want to check his ex's story but I did, and in her story was a picture of a kitchen, that was his kitchen. I immediately broke things off with him and he started playing dumb saying that Idk what I'm talking about and whatever. Eventually it just became this whole thing that I had been going through this past month, text messages came up of him and her talking about how much they wanted to sleep with eachother, and text messages saying how much he loved her. And these messages were actually credible this time. I was heartbroken. Writing this out now I have no idea why I forgave him. But we've been doing okay for the past few weeks. I'm just having a hard time forgetting everything that happened and I'm unsure if I made the right decision. How do I continue my relationship without letting what happened continue to affect me?