>>5148770You cant
I would just tell him “ look man shes going to cheat on you again, and marrying her is only going to give her the power to take half your shit”
And leave it at that, once a cheater always a cheater, Id hate for you to see his ass get raped by the divorce courts, but some men have to learn the hard way
Hell come back and ask for help, once shes taken his house, id maybe offer a place to stay, because hes family. But dont offer any more sympathy, you gave him advice and he ignored it