The #1 reason (co-habitation) relationships break up is money. #2 is sex. It seems since the advent of easy access that more and more men are getting into trouble with partners because of surfing porn and jacking off.
As a female character stated in last night's episode of The Mindy Project, "What's wrong with masturbation? I do it all the time. In fact, I just did during this meeting."
Ladies, I have to tell you something you may not like hearing. You make sex too much like work for us guys. It's not that we expect to lie there and be serviced, or that we don't want to have to put any effort into it at all. But, let me ask you this: Who is responsible for your sexual gratification and release; for your orgasms? You could help, you know. We know your hands reach that far.
And guys, don't think you're off the hook here! You cannot expect a partner to please you whenever you want (need) the release. You want to cum, wrap your hand around that boner during sex.
It's one of the differences I've noticed with women vs men. Sex with women seems to require that we do not stroke our cocks - especially when we shoot that load. But, male partners don't mind if you're playing with your own cock, teasing your own balls. And I've never had a male partner bitch if I grab my cock when I'm ready to cum. And they never complain if I blast that load of jizz all over them.
Yes, it's nice to be able to lie back and let someone else do all the work until you cum.
But, jacking off is part and parcel of a man's sexual repertoire - even when with a partner.