Advice on letting go

I found out my boyfriend of 2 years at the time cheated on me back in November of last year. We have a 1 year old together. I have so many questions I just wanna yell at the top of my lungs. I have asked before where he's met her but I feel like he doesn't tell me the truth. He says he's never seen her before or been with her but when I read the messages he was asking if she was kid free and to come over. We aren't together but Iet him come around because of his child. Anytime he says I love you to me I just can't say it back. Every time his phone goes off, I question us as a family, every time he takes his phone into the bathroom when he showers I can't help but think he's probably still talking to her. I wanna let go, I wanted him to leave me and just let me be. I know what I want and deserve. I don't wanna always feel like I can't trust the person I'm with for the rest of my life but how do you let go when you have had a child together? I mean his family is there and knows what happened and while they have been all so supportive and kind towards me and our daughter, even if we weren't together I don't know how I would move on from the constant reminder. His family said when his ex cheated on him he was hysterical and crying but when I asked him about it he made it seem like sleeping with someone physical was bad but not what he did... Regardless if you slept with someone or talked to them I find it the same thing.