It's a difficult one for sure.
I've been with my partner 4 years, and for the first three, there was no sex, kissing or physical affection, due to him being shut down from MH conditions, the meds he took for said condition, and to some degree i think fear of bonding in that way incase i left him like his ex did. Yes, i got frustrated, as he'd happily "banter" about sex with our mutual friends, including mentioning incidences from his previous relationships, but i'd never had that side of him. I was actually a virgin who hadn't even been kissed before, he's my first real partner. (I was 31 when we got together)
We had a couple of talks about it during that third year, and eventually he mustered the courage to ask for something sexual, when he felt he was ready.
We now have a healthy sexual relationship, but i have thought about what if he closes up again, as he is looking to change meds and it can be a side effect to lose libido.
Leaving him in those 3 years never once crossed my mind, i was content enough with the emotional side of the relationship, but thats partly because i'd never had the physical side. As for now, i'm 99% sure i could go back to sexless, and be okay discreetly taking care of my own needs now and then, but i am very much a need love to have sex type, so i couldn't just get a friend with benefits or have casual encounters, not that i could ever cheat.
Could the DH in this case look in to sex toys to add a bit of variety to self care? There is quite a range out there, and some of the pricier ones are basically a model of the thighs, genitals and buttocks to look like a real person, and can be used in positions to simulate an actual partner, or even a full on doll. It might be a bit more fulfilling than a lifetime of just self hand jobs, but is also not cheating.