OK now that I know a little more information here is my opioion...
NEVER judge someone by there past... it has nothing to do with you!! It should not effect your relationship with him.
But let me tell you why I say that to you, Remember how I told you I had to go through the same thing you are going through with my Finance..?. well I had bad issues as well I was pure and I hated the fact that he wasn't but I loved everything about him... I went snooping about a year and a half into hour relationship and found a picture of his ex hanging inside his safe.. 1 1/2 later... I was mortified!! That is along time to have his pictures of his ex... so I confronted him about it... he told me straight out... she was his first love and he couldn't bring himself to throw it away yet... well I was pissed because 2 months into our relationship he found all my pictures of my ex and he ripped them up and threw them away in front of me... so I was mad and I told him I didn't like the fact that he still had that picture especially hanging up... I mean at least your boyfriends pictures are in a drawer.. well to make this very long story short he burned it in front of me to let me know he was over her... (by the way him and his girlfriend never broke up... her dad hated him and so her dad sent her away with out even saying goodbye or anything... so that is a really HURTful situation)
So he may have loved her ( she was his first)
So he may still have a little bit of feelings for her.. that is OK.. the whole big point here is that he is with YOU no one else just you!! You can ask him why he still has pictures of them together and you can tell him you don't like it.. but let him get rid of them in his own time...
Just keep telling yourself HE IS WITH YOU NOW NOT HER..