He stopped getting hard?

I'm in college and i'm also seeing a college guy. He confessed to me that he is a virgin and I'm not. After our third date we were in bed and we were both so nervous.. i'm usually always nervous before sex and i knew we were going to do it. He was so nervous as well but it was more sweet then awkward to me. I taught him some stuff but the only probably was he couldn't cum. He got close when i kept going down on him but during sex he kept getting soft again. He thinks it's cause he was so nervous and is so use to masturbating. I told him it was fine and say may not be your thing it may just be oral etc and that is okay we can always try again. Has this ever happened to anyone you know or from expericence? :)