I despise cheating. My dad cheated on my mother to be with my now step mother. My mothers husband cheated on his then wife to jump in bed with my mother before my dads side was cold. My sister cheated ion my brother in law with his friend. It's a horrible mess and has hurt me and others so much over the years.
If you're not happy, talk about it. If you're STILL not happy, end it. You've said yourself your husband is a wonderful man. Does he deserve to be treated like this? Throwing away 10 years for a fling. It's a part of life that sex life dries up. It's never as easy or frequent as when you're first together. It's about being intimate together rather than just going at it like rabbits. Cuddle up on the sofa watching a soppy film, have a bath together. Allow things to develop rather than expect yourself to be up for it.

Anyway, probably not the best person to comment, but thats my tuppence worth.