How to forget his past?

My boyfriend and I been together for a while but he was with someone for 3 years before me. They had a lot together. Phone account bank account and apartment etc. Anyway she had a ring with him about 5 months in the relationship which he swears SHE picked out and wasn’t him. Well he also told me he didn’t want anything wit her no kids no marriage. A while ago I was helping him get in his old gmail and his old search history popped up. Engagement rings, having kids, getting her pregnant and much more. I was devastated because he been lying to me for over 2 years. I confronted him and he really still kept it going saying if he wanted to marry her he would’ve. Yet, he was cumming in her for 3 years and still denies he wanted a kid with her. He says he was only doing it because she told him she couldn’t have kids. Yet she has a kid now so I know thats bullshit. It’s like when I confront him on all this he digs himself even deeper into a lie and he says he’ll take a lie detector and all just to stop the fighting and etc. I know its the past, but would you be with someone if your whole relationship is based off lies your gut is telling you? Advice please. Another thing is we were trying to have a kid for a while and so I went to him asking how many times he came in her because obviously if he came in her and me over 3 years none of us got pregnant it’s him. He gives me a bs answer on that too. I just want honesty and can’t stop thinking of everything. Advice please... We just got a apartment together and the fights have been getting worse because I feel like everything is a lie. Advice. He never really talks to girls or does anything now to hurt me he literally works and goes home to me and his protectiveness and all is all I ever wanted in a guy but don’t know what to do. Advice?