She Stupidly shacked up.
She didn't didn't check him out thoroughly during a long waiting period (used to be called an Engagement Period).
I'll bet he didn't give her an Engagement Ring. A sure sign of a creep.
I'll bet she didn't use her parents to thoroughly check him out or she ignored the advise of her parents and/or friends.
She didn't check him out enough to be marital material. If she asked him what he thought about marriage, he probably said "it's old fashioned, you are too sophisticated for that aren't you?" - another sign of a slime ball.
She shacked up with him, finding out what happens to those who do: chaos, domestic violence and commonly divorce down the road.
That's not to say that none of these problems don't happen to those who try their best to be careful. But the chances are significantly less.
For a 99% chance at a successful marriage and family:
Be on the same page about Money
Be on the same page about Parents and Relatives
Be on the same page about Religion
Be on the same page about Children and how to raise them if you want them.
Ask your Parents if they think it is right for you to marry. If parents are dead use the best friends you've got. If the parents are crazy, at least you will have done the right think and proven you are marital material in the process.
Have Pre-marital Counseling with someone you both respect.
For a 50% chance at Divorce/Domestic Violence, Chaos - Shack up - the Devil loves it.
She says he was outraged by scenes where she’d be kissing other men. etc. How intimate of scenes would you permit your partner to stage for a camera?
It’s always been a problem.
And it is not uncommon for two leads in a movie to have an offscreen affair, often which breaks up the old relationships.