This is what I was thinking too. I once dated a guy who admitted to having a pretty regular porn habit. He never finished during sex. Ever. He would always end up going soft for seemingly no reason. It didn't end up working out, but I always did assume that this was a guy who could indulge himself in his own sexual fantasies so much, he wasn't even interested in the real thing anymore. It's not you, porn has set an unrealistic standard for sex that no real person can actually live up to.