Welcome to the forums, alltiedup!
NO! you are not nuts, insane, weird … or any of the similar things. What you feel is totally normal, unfortunately no simple resolution for it.
I too am married and my kid is 8. We are very liberal around the house, all feeling very comfortable in our skins, with lots of love and snuggles to go around. But anything sexual, even hidden underneath the loose clothes, just does not feel right. So … I know what you are talking about. They say once you have kids the life as you know it is over – and to some extent they are right. We want the best for little ones and that includes protecting them from all the evils, growing up being one of them.
Only thing I found works for me is to “play” when he is not around. That might not be as often as I might like – but, when it is than it is good – and I get to keep my sanity!
Stick around, share with us and I am sure you are going to find what works best for you and your hubby. Good luck