Nude pictures of another woman

A few months ago, I found a sexy picture on my SOs phone of this girl he used to like back in highschool. I took it pretty bad but in the end we talked it out and I forgave him. Just yesterday I found ANOTHER sexy picture of another woman.l who's head had been cropped off  and it just broke my heart in two. He claims it wasnt anyone he knew but I felt as if my butt wasn't good enough or something. This experience has caused my self esteem to drop quite a bit. Anyone ever been in a similar situation? What should I do now that this is the second time it's happened?