Jess,

I would have hoped that my earlier reply would have consoled you somewhat...because there are many reasons why your boyfriend could lose an erection during sex. Believe me, many people would respond that if he can't keep hard with you then it's because he's gay or something, and that is the normally the farthest from the truth and allegations made like that could ruin a man.

There are lots of reasons, the foremost being that most guys can really one do "1" thing at a time. So if he gets distracted, even by your beautiful voice asking him a question, it may be enough to knock him out of the moment. It's possible that it is position related, as in he could have gotten a cramp or have some localized pain which takes his focus away. I personally remember (before I lost the feeling in my penis) that when my wife was in a particular position on top where her pelvis was being grinded into mine (clitoral stimulation for her), that it put a LOT of pressure on a point on my body that likely has many veins, nerves and such. Almost every time she did that position, I'd lose my erection. Believe me, it wasn't due to a lack of arousal.

The best thing you can do is to talk to him and support him. Ask him if he knows why he lost his erection. Ask him to go see a doctor. But you definitely have to be supportive. As part of helping, you might even take the opportunity to use the situation to both your advantage. Perhaps you can propose a session for sexual experimentation, where you both try various different positions and such and find out in any in particular cause a loss of erection. The fun part would be that he has to get "re-aroused" and get hard again to try out another position. Eventually you can find if it is position related, which could help a doctor diagnose a specific problem, or as a minimum you both know what positions to not get into because of the negative results.

I hope this helps.