I resolved the situation with the ex by challenging my horrible communication skills, namely my use of sarcasm used as a defense mechanism. There's a fantastic book that helped me out of addiction and unimaginably low self-esteem in my teen years by Dr. David D. Burns called The Feeling Good Handbook. I highly recommend it. It breaks down why we have communication barriers and what we can do to overcome all sorts of obstacles that can hinder the growth of many types of relationships. It also deals with issues of anxiety, depression, etc. Very concise and non-judgmental.
But I digress. Anyway, I resolved my anxiety about this by sending a brief email to him, apologizing for not asking how he was doing in my first message, saying how surprised I was to hear from him, that he seemed to be doing well and so was I, and if he could drop me a line.
I feel a million times better now. It's out of my court, it's not weighing on me, I feel like I took it towards a path that I normally wouldn't have. I need to break my old habits if anything is ever going to change in my relationships. So this is a start, regardless of what happens with this particular fellow.