Can i have some advice?

My boyfriend and i have been together almost 4 years now and i love him to death. But lately i've been having some problems trusting him. I found on his computer a thing for scarlat johanson naked then on his iphone said kristen bell naked but he swears to me that he never did that he even broke down crying and i've never had these problems with him b4. One night he had all his buddies over and his lap top was with all of them and him and one of his friends got into a fight and he left his laptop and phone in the living room with his friends because he just went to bed. I do have to admit the that the naked girl thing was mixed in with the other stuff that his friends were looking at. My boyfriend is the best and he is always honest with me and has never done anything like this. Should i believe him that he didn't do it?