I got a response from him and an explanation from him. I was not expecting as much, but it appears we have both matured.

As others have pointed out, the chances of us being friends again look like they might not happen. He mentioned that I'd done something that I do not recall doing (although it doesn't sound beyond me). If it did happen it was because of a terrible immaturity and lack of intuition on my part. Embarasses me to think about it.

It feels really really good to hear from him and to have him at least give me an inkling of what was happening with him at the time. I was pretty much in the dark although in retrospect I had started to suspect that he was deeply wrapped up in his own conflicts (which he now confirmed). I think the most important thing he expressed (and it really brings tears to my eyes) is that in that year I was about as important to him as he was to me and for terribly similar and yet starkly different reasons.

I really did not expect him to go into details. He was always very private when we knew each other.

This is surprisingly a best-possible result.