Why does sex have to stop in a marraige?

I know it's been asked a million times, but really think about it. Why does sex have to stop when you're married? When I was dating my wife, I couldn't keep my hands off of her. We had sex at least 3 times a day every day. Sometimes, we would purposely have quickies during our lunch break. But it's ironic that after I said "I do", the sex said "I don't". It's sad to me how Single people have more sex than us married people. Yes I know raising children is a GIGANTIC sex killer. But it still baffles my mind, because when all your children are in school, that gives you 8 hours to tear each other up, but nothing happens. Which is sad because when you had a 30 minute lunch break, you two would go at it like rabbits. Just some thoughts on my mind, I don't know if this is a rant or not.

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