My 20 year old boyfriend is having problems keeping his ?

My boyfriend and I have been going out for almost 7 months now, were both virgins before each other, and have recently started having . We had had maybe 10-12 times before this started happening, but about a week and a half ago, he lost his while we were having . He immediately got upset and refused to keep going with anything, making me upset as well. He is concerned something may be wrong with him, since the past 3 times since then we have done anything, he cannot keep an , even if we are not having . He says it has nothing to do with me, because he is attracted to me, but should I believe him? Also, should he go to the doctors? Because he is concerned about that as well. We don't know what to do! It is making us argue and creating a riff that is distancing us.. I don't want to fight about this anymore. I want him to know that it isn't that it's happening that I get upset over, it's how he reacts to it. What should we do? Help!