For starters, don't look at things you know are going to make you feel bad, like your boyfriend's photo albums of old girlfriends. How did you expect to feel after looking at shot after shot of your guy having good times with other women? Your reaction is normal, and you should have predicted it. You knew he dated others before you, right? Of course it sucked to see pictures of it and read e-mails between him and old girlfriends.
Look, anyone can work herself into an insecure frenzy by obsessing over the past loves of a partner. Maybe it is insecurity that makes you do dumb things like peruse his photo albums in the first place, but doing so only makes the self-doubt that much worse. Your boyfriend is right: everything in those albums and e-mails is the past, and you have to let it go. He has. If he wanted to be with any of those women, he would be with them now, wouldn't he? But he's not; he's with you. Why? Because he wants to be with you. Nobody has a gun to his head.
You are his partner today, and he says you are his future, too. Don't waste the present and the future obsessing over something that doesn't matter anymore: the past. Let it go, focus on today, and don't go looking for things that you don't want or need to see.
Thanks for the question.