Sexual emergency

My boyfriend and I finally had sex oct.31 and it wasn't what I expected, he couldn't get on hard for anything and when he finally did, it was for all of about 10 minutes. We've only had sex 3 times and the experience has been the same. I don't understand what could be the reason, I asked him if it was me, and he stressed his opinion, that he was very sexually attracted to me. So with that being said I'm at my wits end and although sex is not that important it can be a key ingredient, in a relationship where both people like sex.