Advice

So I live with my bf. I go through his phone sometimes because he's cheated on me before, it's been a while but I'm still trying to gain my trust back. I've come a long way, but I still look at his phone just to ensure that nothing bad is there. The other night his sons mother texted him saying "I won't stop until your gf has a ring on her finger, until then she has to share with me! I know you want it, don't even deny it". So I saw that and got upset, he texted her back in front of me saying this has to stop my gf saw this and she's upset and we should only be talking about our son. So she got pissed and left him a voice message the next day, I didn't know about it til last night. Last night I went through his deleted voice messages and found one from his sons mother, talking about how he responded to her text the other night. She said "I don't get it, when you want to flirt and talk dirty that's okay, but all of a sudden SHE (me) is there on a week night?? How the hell was I supposed to know she would be at your house and see your phone, you told me she just stays there once in a while and you talk to her once in a blue moon.  So that's wrong. So I don't want her around our son anymore, if she's there then you won't see him anymore". Well we had him this weekend and she was ok with it, but I want to confront him. Cause now supposedly he talks dirty back to her when all along I thought it was just her coming into him. and I want to ask him why he would lie to her and say we talk once in a blue moon when really we've been together for 2 years and live together. But I don't really want to say "hey I went through your phone and your deleted messages and found this so explain it to me". I know he will get mad. I don't want to seem crazy. Is there any way I can bring it up without seeming crazy?