You know, I read just the first page of this thread and the question was asked by the OP about what to do downstairs... nothing. Do absolutely nothing.
He's not there to occasionally get off when he gets hard, he's there because he has no place to recuperate from this accident. The fact that you offered to take 'CARE' of him show a level of character seldom found in our society today and should be commended. If he is straight, he's not going to want you to take care of his sexual needs and the fact that you are asking makes me wonder about your profile status and that being said just give him the best care you are able. Watch the nurses and ask questions. When it comes time to wash Mr Happy and his surrounding kingdom, just do it. He may pop a woody but he's not going to want you to finish him off.
Again, you should be commended for opening your home to your friend. I hope he recovers quick.