True, trying too hard, or high expectations can cause performance anxiety in men - have you tried reverse psychology?
Dress provocatively, then tell him he can't have it. He may just have a low libido, it happens, and working a lot really does leave you tired and less horny - sex is mostly in the head.
Help him change gears after work, let him relax a while, take a shower, shed some stress, don't bring up sex for a while, you can masturbate to relieve your own frustration.
Also, have him try zinc supplements.