VERY long story short:
Been divorced four years and couldn't care less what he gets up to now (he's not speaking to me anyway ATM as I put him straight when he started trying to push me around again).
He had affair with AP, left when I threw her out. I asked him to come back after five months, he did. Things still not right, four years later I tell him to leave after he finally admits he doesn't love me anymore. A few months later, I find he's with a woman whose mother he has visited every five weeks whilst 'getting his hair cut' - for the whole day. There's more but mostly not relevant.
So far, so what, you might think....
The thing is, this week I've found that the OW's mother has been spreading rumours - that I was the reason we broke up, as I had an affair. 
Even this I could attempt to ignore (I'm a fairly proud person, but for the record I haven't even got back into dating yet as he broke my trust so badly) BUT it was my DF who had this rumour repeated to him - my parents live near OW's mother.
My parents won't tell me exactly what was said, so it can't have been flattering, but I do know my DF ended up saying 'look, that's my daughter you're talking about'.
Beside the obvious (that there's nothing like blaming the other party for hiding your own guilt) I'm bemused as to why there is a need to say anything at all after all this time.
So MN jury, WWYD? Ignore, write a letter, email xh, solicitor's letter (my knee-jerk reaction)...