for what is worth, I am a man with very similar issues to the OP's DH.
I love my wife deeply and we are a great family, rarely disagreeing over much, I enjoying sharing all lifes journey except one, I have a phobia when it comes to sex. I do not use the word phobia lightly, it is a mental 'wrong', or illness that in many ways stops me from being normal. It is completely irrational and unwanted, I would give anything to be a 'normal' man. I ( and we ) have tried many things, from counselling to medication to treatment with a psycho-sexual nurse but none has brought significant change, my problem was wired in my brain as a child and there is no magic pill or prayer that can undo it. Obviously this is just my experience but perhaps the OP DH thinks the same, it must be very difficult for the suffering partner to understand but this is how I feel/think:
I find my wife sexually attractive, I'm even more normal than that, I find many women sexually attractive, the abnormal trigger only fires once ive got my clothes off.
I understand that my condition causes my wife significant pain, I am weighed down with guilt that I am hurting someone I dearly love.
It is very selfish of me to be the way I am, and expect my wife to remain faithful. It still hurts just as much when she has affairs, but with the added battle that I 'shouldn't' feel hurt, I deserve it after all. Except it is not something I have control over, I can't just turn it on and off.
Notfootball, the only solution is the careful and planned dissolution of your relationship, it is the best thing I could do for my wife, to release her, I don't have the strength or courage to let go of someone I deeply love, let alone my worries of what it would do with the kids, it is though, imo, the only answer :( I hope you manage to work things out