He’d be very careful to keep an eye on them, watching for their symptoms, sometimes even better than they do.
They in turn let him know if they’re having trouble with something, and what they’re doing to try and overcome it.
He’s definitely going to make sure their living arrangement isn’t dangerous for his s/o, and that they can move around the place on their own on their good days, and so that they won’t hurt themself on their bad days.
He will sort of hover over them through frequent texts through out their day, and phone calls. This would bother his s/o, but they’d understand his concern.
All in all, he’d just be there for them, and willing to stay by them through out their illness.