I am glad you agree with God, even though you have no idea what God actually has to say about it. Matthew 19:9 "And I say to you, whoever divorces his wife, except for sexual immorality, and marries another, commits adultery, and who ever marries her who is divorced commits adultery.
What this man did was sexually immoral. According to Christ, she has grounds to divorce him. Cased closed.
Unfortunately, we are held to our vows. That means, regardless of what anyone else does, we must keep them.
When someone makes a vow with God, it is usually "in addition" to what was expected of us. Case in point, vows of celibacy or vows of poverty. God never says we must do either, but when we do, we are held to them until death.
If someone vowed with God, "Until death do us part", then that is precisely what must be done.
I believe many women who love the lord more than thier spouse usually are more forgiving to husbands with the exception of abuse verbally or mentally.
Mel Gibson's wife has put up with her husband's habitual drinking problem for years...