Say nothing unless you’re 100% certain but ignore advice to keep quiet if you do know.
Ever heard of the saying "shooting the messenger" tickingbird? So far OP has only "a gut instinct" which may turn out to be correct, maybe not. Even if it does turn out that the son in law is a lying, cheating ratbag, would you really want to be the one to take your "evidence" to your daughter and present it to her? Do you think she'd thank you? Why put yourself in the middle of someone else's marital problems? Hard as it is to stand by and watch it all unfold, keep out of it and just be ready to support her IF she needs you. Nobody likes a meddler.
The Devil In The Family: The Fall of Ruby Franke - BBC IPlayer
Labelling cake tins or cutlery you have loaned.
Daughter not allowed to know new baby’s name until she visits him


