Have you tried to give her a day to herself without the expectation of sex? You take the kids and let her have a day to pamper herself. Give her money to get a haircut, mani/pedi and a new outfit? If she is a SAHM she might be overwhelmed and stressed. My husband and I are in the other side. When my boys were younger it was like one-more-thing I had to do. They needed me all afternoon when I got home from work. The house was a mess and I was working, shopping, taking care of them and when he wanted to have sex it seemed like a chore. We had to work at it and he needed to pick up the slack on some things. We worked through it by we still have our days. My point, show her you care without wanting sex. Try to figure out what the issue is.