Oh this can be a problem. My x husband was a "walking erection" . He could not get enough sex. Every day sometimes twice a day...I can say I did have a "beautiful complection" then, as they say sex is good for the skin and heart and lots of other stuff. At first it was coooool.. But after awhile it got to the point I could not stand him to touch me.
I guess my best suggestion would be to have a heart to heart talk with him.. Maybe explain to him that there are times you just do not want sex and that does not mean that you do not still care or love him.. I think if he understands that you are not rejecting him, that you just are not in the mood, he may understand better.
On a lighter note, maybe start cooking more food for him.. I have learned over the years that "food" side tracks mens. Thinks (smile) they can only have one thing on their mind at a time. And when they smell food, they pretty much forget everything else.. including sex.. Oh and usually after chowen down food they fall asleep..