I saw with my own eyes recently, my man was completely drunk and incapable of an erection but he was very horny. I can't do anything with a drunk penis. However, he managed to jack off and have an orgasm with little to no hardness. I'd look into his diet and try to figure out WHY he's not getting hard. Horniness doesn't always mean erection, not if there is a dysfunction.
Definitely make sure it isn't due to drugs or alcohol and work from there. It's not always emotional.