Caring for a loved one whose prostate has been removed can be very tricky, as there are emotional as well as physical elements to it. Physically, you need to care
for him as anyone who has had a major operation. Make sure he has plenty of rest and fluids, and his pain is managed. Work with him on the therapy schedule so that he can get back to gentle movements, regular digestion, and walking.
There could be a few other physical items to deal with. If he experiences incontinence (leaking of urine), you can offer him adult incontinence briefs, available at most grocery stores. His stream of flow during urination may also be affected (decreased or inconsistent), which is natural but there is little to combat that. Sometimes, the surgery is followed by impotence (inability to have an erection) and/or inability to ejaculate. This sexual component can bring not only a strain in the sexual partnership but also emotional challenges too, as he may feel inadequate, "not quite a man," or no longer useful as a man. If trying to have relations is awkward, you can start by touching and hugging each other. Try to laugh and keep it light if possible -- a few good joke books or internet sites can help.
If you are his partner, I encourage you both to go to counseling to work on this component together. This is not just his circumstance, it's his loved ones' and his partner's, and he should be willing to do this with you. If not, go yourself. Some counseling centers offer the therapy for free or a reduced cost. Sexual relations can be very healing in their own right for both people.