Hopelessly restless

I've been in a relationship with this guy for three months now. We spend almost every day together (neighbors) and have grown really close. He's a very honest person and that's something I love about him. When we first met he let me know that he cheated on his child's mother with a woman who is claiming he is the father of her 10 month old. He denies paternity because he says that she was seven weeks pregnant three weeks after their first sexual encounter. She also admitted to having sex with two other men around the time of conception. Despite knowing this, he stayed with her throughout her pregnancy but did not claim her child. He told me all about his irresponsible past and how this particular woman always managed to work her way back into his life. Naturally, I ask about her and he always lets me know when she calls and what their conversations consist of. Recently, their contact has become more frequent and he's less forthcoming and it bothers me so much that I've stooped to going thru his phone. Given his history with her, I'm uncomfortable with their relationship. He says he plans on exing her out for good after he gives her a paternity test but I still don't see a need for him to communicate with her beyond the test. I've hinted my discomfort but to no avail. Recently he has become a little more defensive. I'm seriously confused on what to do besides stop snooping thru his phone.