Naked pictures of other girls.

Last night I was on my boyfriends phone. I will admit that I was snooping, but I had a feeling that he was hiding something from me. I had seen some pictures of boobs on his phone about a month ago when he was showing me some other pictures and of course I asked him about it. He admitted to me that he still had pictures of his exes and that he kept them as a 'security blanket'. I was, of course, upset about it, but he promised me that he didn't ever look at them and that those few pictures must have gotten on his phone when he synced his iTunes. I really wanted to believe him and he's never given me a reason to doubt him, so I let it go when he promised he would delete them off his phone. So last night I looked just to see if they were still there. Instead of finding those pictures I saw he has whole albums of naked pictures of a lot of his exes, and even worse a bunch of pictures of some other girls with dates on them from last year. There is also a picture of a positive pregnancy test that isn't mine. We've been together over a year and I'm 37 weeks pregnant with his baby. I don't know what I'm supposed to do. Should I ask him about it? I'm afraid he's just going to lie since he's now preven that he will just lie straight to my face. I was so sure he was different. Am I just an idiot for believing that not all men are horrible pigs?