Hi Mulatto. Welcome to the Cellar if you haven't already been welcomed.
About your issue with your boyfriend, there's a couple of details that might help people give you better advice. For instance, how old are you both? Have you also been sexually active in the past or is he your first lover?
From my perspective, if I'm honest, I would have to admit that sometimes I do think about the women my husband has been with in the past and wish that I'd been the only one. I've never asked him, but I think he probably wishes the same thing about me now and then. It doesn't ever get me down too much though because I have to realize that he is the sum of all his life experiences prior to me. Without even one of his adventures or pitfalls, he wouldn't be the same man, so in effect, I really should be thanking those women for the gift they've created.
Remember, the past is simply history, and it doesn't apply to your relationship unless one or both of you bring it back to life. You know that if any of his previous lovers had been the one he wanted then that's the one he'd be with. He's chosen you. Maybe you should be asking yourself if there's any reason why you think he shouldn't have chosen you.
In my experience, it's often good to talk about these things with the person involved just to let them know your fears and reasons for them, whether they seem silly or not. You'll know he really is the one when he simply assures you that you're the one he wants and no other.
Good luck with it though. Relationships can be tricky, and often a lot of the pressure on them is that which we exert ourselves. Maybe try letting it off a bit and see what happens.