Boyfriend Troubles

What do you do when your current boyfriend keeps talking to one of his ex girlfriend but you have told him several times that you didn't want him talking to her for obvious reason and he still disrespects you and does it anyway.... I've read text messages in his phone that haven't been to bad they just talk or whatever but the most part he has her in his car when I'm not around. He has cheated on me with this same girl in the past and I still don't trust him. I haven't said anything this time but I see this mess in his phone and I become distant and stand that I'm letting him do this to me again