I did it. I answered Mr Ex's e-mail. Receiving no further advice (not really), I decided to trust my instinct (which I probably would have done even with legions of advising me to do the contrary). I just told him that I didn't think that I should answer his question at this stage in our "just friendship." Yes, that's what I'm calling it--just friendship. I told him I would in the future, but that I didn't think our present relationship could handle that kind of "colletive soul-searching" right now. Yes, that's how I put it--collective soul-searching. It will be interesting to see how he responds. I hope he understands.
Really, I don't owe him an explanation, though. Not as to why the relationship became unhealthy for me, nor as to why I don't want to answer his question now. But I will give him one and I did give him one for the very reason that I cannot address his concerns presently: our past together.
I'm happy with my decision(s). I hope he kind find some comfort in it (them), too.