Super low sex drive!!! What should I do?

My husband and I have been together for 10 years and we have an 8 year old daughter. I've always had a semi low to mild sex drive, maybe even medium at times but my husband is a nymphomaniac(meaning he wants sex 24/7). Lately my sex drive is nonexistent to the point I don't even want to give in and just do it like I sometimes do. Don't get me wrong once we are actually having sex its great!, but trying to get there is ridiculously hard for me. I don't beleive I'm under too much stress and we have a happy relationship no issues. Hubby is so understanding and has been for years but I don't want to keep doing this to him any advice, comments, concerns, or anything would be greatly appreciated.