Boundaries work. They may not get your H to stop his A, but they let him know what you will do if he doesn't.
This is the short version of what type of boundary needs to be set: W"H, this is not working for me. End all contact with OW starting right now or I will file for D"
"What is best for my kids is best for me" Amor Fati Link to quotes: https://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2879712