It didn't happen with my wife, but while I was dating an ex-girlfriend.
We went to a party and she told me there also will be her ex-boyfriend. She pledged me those usual things about not to get jealous, and not going beating the guy if he just pass by to say a hello etc.
Well, but for my surprise the guy indeed came over us to talk, but he firmly presented himself just as a regular friend of my then girlfriend, you know, really trying to sound proof as he was merely an ordinary friend and such. The guy was sweating non-stop, nervous as fuck, his voice trembling and he couldn't keep an eye contact with me or with she for more than one second.
Then he made a question about us two going finally to marry or not, and I decided to put a end over his self-torture and I replied that we would let him know if that day came, despite him being an ex-bf.
The guy seemed almost to cry, and to be honest I felt pitty for him.