One of God's great tricks is that the females have such a lower sex drive than the males. It makes for much angst in the relationship sometimes.
My wife and I have been married 14 years as of this month. We're in our mid-thirties, and we haven't slowed down one bit - still about twice a week, give or take. BUT, her interest in the activity has dropped off dramatically, and now it's as much an accommodation as an interest for her. At least she's still accommodating. She's a good egg, my wife.
I can not stress enough how much damage it would cause anyone to cheat - the second you cheat your relationship is over. I'm not singling anyone out here and I'm not trying to be a punk about this, but just realize that cheating is a one-way street. Once it happens the relationship can never, ever go back to how it was, even if the other party never finds out.