Well, so much for that.
Although it had blossomed from a "dating" story to a friendship (and no longer really belongs in this sub-forum), it seems that some hidden tripwire in my Ex has been set off, and he's gone completely silent.
It followed a really great, friendly platonic afternoon (one of many we've had in the past 6 months) where we chatted, had food, played trivia, and he left my place all-smiles. Then, the next morning he called ostensibly to "thank me", but his phone demeanor was very curt and I hung up knowing that something was very, very off with him. After a few days of the silent treatment he called again to say that while he had left my place thinking what a great time we had, by the next morning he had reconsidered and realized it "wasn't as fun as he thought". He had a bunch of complaints that came completely out of the blue, many relating to past conversations or events, and most of which really did not make sense (to me at least).
It's been over a week, he hasn't reached out since, and I won't pursue getting in touch because I gather he wants space. I suspect the friendship is over in his mind.
Too bad. Things were going really well.
Sorry it happened like it did for you .