Thanks, Everyone. I haven't responded yet, and am not planning to. What I may start doing is creating opportunities for him to interact with me positively, like post pictures of the cat on FB (my friends love me enough to tolerate some cat photos, lol) or other similarly innocuous things. I don't feel comfortable asking him anything directly, because he tends to feel interrogated at the best of times, but it might be a way to build a bridge. I typically don't post on FB at all, so this will give us some opportunities to just be on neutral ground with each other.
@ busywend: Not at all sure how to take your comment. I don't think he sits around and wonders if I'm alive or dead, honestly. He may sit around and wonder why I'm not chasing after him, but I don't believe he thinks about me, per se, at all except in relation to him. (That's not bad or good - I didn't think about my parents as people until I was 30 or so, so I wouldn't expect it of him at this point.) I know he's ok because I see FB proof-of-life postings. Again, not sure what your intent was.