Relationship struggle

I’ve been dating my boyfriend for a year and 6 months now. Me and him have talked very seriously about getting married and everything we have the same life goals. My parents have even agreed that we can live together and get married as soon as I graduate college, and this is all my decision my parents never even influenced this. Either way we have broken up 2 times both of which he broke up with me. The first time was at 6 months, he just didn’t know if I was the one, a few days later he came back begging for us to be together. And during those few days he immediately hung out with a girl and she kissed him but they had both just gotten out of relationships and missed their exes. So he came back to me and that girl went back to her ex. The 2nd time he broke up was at our 1 year he was like I don’t think our morals/ family’s are the same so I don’t think it will work out plus I want to go to Utah for college. 2 weeks later he came texting me asking to be friends and then we talked on the phone and we both revealed that we still want to be with each other. During that time we were separated he had applied to a college far away but took it all back and applied to the college close to home that we both originally planned on going to. Then 2 months after we got back the 2nd time things were going better than ever until my friend told me some 2 girls that I know of had said something about that my boyfriend has sent them stuff a few months back (dirty pics) and talked dirty. I investigated, I already knew his social media passwords so I went on one of his apps and found old texts from when we were dating at our 9 months about. It was dirty texts from a random girl from really far away. Another thing I found was him telling his friend that if I ask if my boyfriend drank or smoke to just tell me he didn’t (I have told my boyfriend I don’t want him drinking or smoking so he’s not supposed to). Either way I confronted him about everything and at first he tried to lie and said believe what you want. But then I showed him the proof and he admired everything else. He agreed that I could look at his stuff whenever I want and that I’m the only person he wants to be with and that he did those things before and those things happened many months ago. And he’s religious and even swore that if he ever broke up with me or cheated he swore himself to go to the devil. So a few months later in to New Year’s Day a random girl texts me saying that many months back her and him would sneak out in his car and do some things like kissing but not sex. And she said she could only give me proof he added her back on Snapchat and she was asking me if I knew his password and everything and if I could unblock her and stuff. So I tried that night but I was with him and he got super upset and was like why are you trusting that psycho girl she’s a girl who tried getting with me a bunch of times and she’s crazy. And he said I’m no longer allowed to have his passwords because it’s breaching his freedom and privacy as well as it’s just showing that no trust is being rebuilt. And that we cannot build our trust back if I’m consistently wanting to know what stuff is on there. So now in present day I still sometimes really just want to know who some of his new guy friends are or even just what goes on, on his stuff. Basically we still have our plan we wanted to get married this summer it’s just honestly how do I build trust again and how do I get over this hump of thinking he will cheat on me. Which all I know 100% is the most he has done is sexually text and apparently only sent 1 mirror pic with underwear on but the girls sent full stuff. And there is the chance that the random girl on New Years he did actual physical cheating with her but I don’t know because he denies it and nobody I know knows her. And she couldn’t remember exactly when it was like at least the month would help, all she said was it was a few months ago and that could have been when me and him broke up for 2 weeks. I don’t know at all. All I know is that me and him are perfect in every way together, besides this whole me kind of not fully trusting him. In our relationship it used to be I fully trusted him but he didn’t trust me even though I have never done anything and he just had jealously problems, now ever since I found out about the past stuff I don’t trust him fully but he trusts me fully and there’s no jealousy issues anymore. Please someone help I need some advice.