He can only control his behavior.
She shouldn't have started a new account behind his back like that communication is already failing and that already starts them on the wrong foot, but they need to have a real discussion about their respective needs and boundaries and whether they're incompatible with a relationship.
I suspect my partner is cheating for a while now, but she denies it? What has turned out to work for me and I started where you did is to actually inspect my emotions.