After my divorce my DF continued to stay in touch with my ExH, playing golf regularly, going for drinks etc. I was very hurt and couldn’t understand it. I’d told my DM all the details so it felt very disloyal of my DF. Then years later, after my DM had died, my life was sorted, and I was having a proper chat to my DF he suddenly asks why I left my ExH. Turned out DM had never passed on the details and reasons. Dad was horrified and immediately cut all contact, after giving him a piece of his mind. My ExH was mortified and there was an added bonus that his support for my DCs at uni stopped being a big issue.
OP, I wonder how Twattoo would react if he got some home truths from your DF…?