It hurts so bad

So two years ago, my bf and I were in a very HORRIBLE spot in our relationship. I was pushing him away because I never trusted him even though I personally didn’t have a reason not too. Anyway, many months later I went through his phone, hoping to NOT find anything so that I could build some trust in him. I found old messages that he was sending another girl during our rocky phase. He was asking her for sex. I know this girl personally, we all went to school together. She would flirt with him in front of my face and he ignored her because he swore he wasn’t into her and that’s exactly who he ran too when things went bad. We did talk about that situation and he apologized and swore that was the only time. Aside from that I didn’t find anything else. Whatever trust I was trying to gain was, and still is, just gone. Even after two years. My trust for him is on the floor. We’re talking about marriage and looking at apartments together and I’m just hurting. Every time I see him on his phone, I die a little inside. Because he cheated through his phone, from what I know, I don’t trust him with it but of course I can’t tell him to get rid of it, that’s not reasonable. He hides his phone from me. Takes it everywhere with him. I can barely touch it. Always has it on silent. Tilts it to side when I’m around. I don’t know what could build my trust in him, I don’t think anything can. But I feel crazy ending things when I have no proof of his disloyalty these past two years.