Sorry, I got hold of the wrong end of the stick.

Mmmm, tricky one Rhian. I would certainly respond as he could be quite hurt by your non- response to his hello message. However, I would keep it friendly but a little formal, including the first question I would put after saying Hello and How are you, is 'how is your wife? and the family?' or 'I hope you and your wife are both well'

I know the above is stating the obvious, but at least he will know that you know and assume he is still happily married. Just because he is a man, albeit one you dumped 30 years ago. there is nothing wrong at all with chatting to an old aquaintence. Only if you allow it to proceed any further than friendly chat, will be when the problems start. I'm sure you are savvy enough to gauge things if he starts to get more personal and 'inviting'.

So, I would happily respond and say hello.