How do you trust your S/O again after something traumatic

Okay so...when I was pregnant my boyfriend/ fiancé cheated on me..it was horrible and I was extremely depressed and this went on for 3 months of course I found out almost a month into their relationship (I had a feeling but didn’t have proof yet) so anyways they break up because the whole time he’s messin with her he’s still messin with me....so she dumped him and we went on with our lives and were happy, then we had to move so we did and a few months later he cheats on me again (still pregnant) I got so depressed I moved in with my mom till I had my daughter which was for a month...the day came where I had her and the NIGHT I had her he lied to me and left the hospital to go stay with her. I was livid. Sooo she finds out he’s STILL messing with me and leaves he comes back and we’ve been together since..this was back in July when he came back. He tells me time and time again that I’m the only one he wants and I have his location on everything and his passcode to his phone so I can go through anything I want when I want. But I just cannot find it in myself to trust him or even try to....I mean I try so hard but my mind just messes with me and makes me go literally insane...ever since he cheated on me I’ve been so insecure and think I’m so ugly....please help me and give me advice..