When I've been in relationships there always has come a point when we're not doing it as much as we were when it was all fresh. Then I feel the need to fap occasionally. I used to feel guilty about that and try to stop, but more recently I've realized it's natural. I don't keep it from my girlfriend, but I also don't tell her how often I do it.
She'll ask sometimes what I've masturbated to. It's usually some kind of photo or video porn, but it could be some hot girl on TV or an especially well written hot story.
Now that I'm older, I really need to release my swimmers or face the prospect of prostate trouble.