We here of course don't know all the ins and outs. For one, we don't know what you said to him in that letter...maybe he had reason to block you??? Whatever the case, just let it go and to this outsider it doesn't sound like it would have ever been a good mix. Try to learn from this experience by being honest with self about his and your behavior. About both of your behaviors. Realize that everyone, including this guy, including you, has a full plate, is just trying to survive. Let it go...wish him well outloud. Wish yourself well outloud. Talk to a therapist if necessary about how to let this go and also about your panic.

Sincerely all the best to you.