Well, I can only say from personal experience that when I was in a lot of pain over some embarrassing physical issues, I really didn't want to have to deal with or talk with anyone. People are of course all different, but I'm of the ilk of wanting to say "Please, I feel really bad, just leave me alone."
The idea ehbeth gave of sending a real live card is good. One card, one time.
It's hard enough feeling awful and being around those who know you well. I would think he really doesn't want to have to put on a brave front with someone he likes, and is looking at down the road getting involved with.
How much space?
All the space he needs. From the little you said about him he seems pretty intelligent and sensible. He's not going to forget about you, and will appreciate that he was able to handle all this in his own way.