I think the first thing you should do is talk to him about it. You don't sound angry, and so try not to come off as being angry to him. But you should definently talk to him about how you feel. Men can be very dense sometimes, and chances are that if you do not say something, he will never know how you feel.
You also have to understand that she probably means a lot to him, especially if he has a daughter with her. The part of his life that she was in was major for him. Marriage is a big thing to enter into, and an even bigger thing to end.
You should probably be happy that there is not a bad relationship between him and his ex-wife. Things could be a lot worse.
I think that you should also be happy he is not trying to hide that stage of his life from you. I think that he is trying to share with you those memories, which probably means that he looks back upon them with fondness, and wants to share this happiness with you.
I understand how you feel when you look at pictures of her, and of them together. Try to keep reminding yourself that he is with you now. The paticular stage of his life is behind you. And you are his present and his future, instead of his past. He wants to be with you now; he wants to move forward in his relationship with you.
But first and foremost, you should really talk to him. Its not going to be easy to bring up your feelings to him. But once you do, i'm sure you will be very reassured and content.
I hope everything works out with you. And that my advice helped atleast a little bit.
