I like being married. Don't/won't cheat.
I think sex with a partner you know and love is way better than strange sex. She knows what I like, I don't have to fumble around getting partial satisfaction (same with her). It's very easy to communicate in bed...we know what we like and we don't have to putt about figuring each other out.
Plus, the reason the sex is good is because I genuinely love her, and like being in her company. She's a great lady, a great mother, my best friend, and I'm better for having her in my life. That's sexy too...to know that you get to be with someone who's great for you.