How do I learn to let this go?

So my boyfriend and I have been dating for almost 6 months. From the beginning I was always alittle nervous about him cheating on me because when I first met him he was cheating on his girlfriend with me (I didn’t know he had a girlfriend) ((I soon found out she cheated first and the we’re ending anyways)) so I always checked his phone and sometimes i found iffy things but it wasn’t flat lut cheating so I let them go but they caused me like mental issues because I already have depression and anxiety and this wasnt helping but he was a good and loving boyfriend so I often let it go. In February he got into a car accident, he was fine but he was looking for a new car. He sent me a screenshot of some of the cars he was looking at and I saw he had a whisper app icon which made me nervous because whenever I checked his phone he didn’t have whisper meaning he was deleting it and he met me on whisper. So that weekend on Saturday morning I redownloaded jt on his phone and restored his account and my heart sank. He was posting about open minded girls and if anyone wanted to see his dick and he had lots of messages but those dont reload so I didn’t know but you could imagine the nature of the conversation. I started crying really bad and he woke up and asked what was wrong. I asked him about one of the posts he made and he said it could have been from a long time ago and I was like two weeks isn’t a long time and instantly he started apologizing. Him apologizing just broke me because I realized that all of my concerns were real and he wasn’t as perfect as I thought. He never met up with him so I stayed by it looked really bleak. Between then and now he has genuinely apologized and cried and poured his heart out for me and now when I check his phone there is nothing there I’ve when I check it impromptu so he doesn’t get a chance to delete things. I don’t 100% trust him and sometimes even have those thoughts even with nothing to back it and it’s ruining my life because I’m always paranoid about it. I love him so much he was my first love and first boyfriend and I want to let myself fully let go and not be afraid during the week when I’m not with him. I want to be able to trust him and learn to because I really believe he is fully committed to me as he’s told me. (He’s also told me he wants to marry me) I want to have peace any tips?