Soft during sex? Is it me?

Stora • treat me like a princess, fuck me like a whore

So..the guy I hook up with, when we're having sex, suddenly goes soft without even realizing it. We've messed around before and I've gotten him to get off, but when it comes to actual penetration we last a little while and then I notice he's soft and he hasn't came.

Would this be a problem on his end, or am I doing something wrong?