Boyfriend might still be cheating?

Hi there, I’m writing here today because I need some advice. I 20f have been dating my boyfriend 21m for 7 months now and I’m also 21 weeks (so 5 months) pregnant. Now here’s the thing, he was cheating on me for a month and a half. I caught him and decided to stay with him because I love him and thought maybe he would be truthful and loyal this time after lying to me for so much and hiding stuff and well not being loyal. Also I want to stay because I want our kid to have him in their life. However, the issue is he just hasn’t been seeming like I can trust him. He still hides his phone, sometimes I asked him to do something so I can get a step forward to help myself heal and he dodges stuff until he wants to do it, and I feel like he never takes my feelings into consideration. And I do have her number I’ve never talk to her before, but a part of me really really wants to talk to her to see what he was so fascinated about, to see why she did what she did because she had found out that he had a girlfriend and a baby on the way, and still decided to be with him. I know which probably not a smart idea, but I feel like if they were somehow still talking and I asked her to show me proof I feel like she’d have no reason to lie to me about it because then she could have him for himself. And we’re thinking about moving in together and it’s a really big step financially for me because I’d be helping him and I don’t want to be stuck somewhere with him or financially stuck if he is still cheating. Any advice on what I should do, if I should talk to her?