Sounds to me like he's a bit of a sex addict considering the fact that he needs to jack off on top of how much sex you guys have already. But hey - nothing wrong with that as long as he's a functional human being and jacking off is not the only thing he does.
And like many posters above me have commented, masturbation requires a lot less effort and he can be done pretty quick. That's probably why he doesn't come get you every time.