My boyfriend used to have the same problem. When we were about to "do it" and all of the sudden he wasnt erect anymore. This is was frustrating for both of us. It seemed to me he was just stressed out and thinking too much about other things. I looked online too see if he may have any type of condition but he didnt match the symptoms I had read. I told him to just relax and I gave him massages to ease into the mood and all that good stuff. We tried again and it seemed to work. So my advice to you is to just relax and think about what turns you on when your with your girl. Do stuff to her to arouse you. He seemed to perform better during sex an was more confident. Well I hope this helped out. Good luck!