Making Him Come?

My boyfriend and I have been dating for a few months now and we have sex on a regular basis. Both of us are very attracted to each other and he is always extremely excited when we get down to it. We have a really good rapport established so I know he's telling the truth when he says he's having a good time — but he's only ever actually come for me once. 
A) should I be worried about my performance? 
B) any tips?