She is a way better person than him. That I agree but you are still way off and biased on your perspective.
"He chose to marry her knowing her family was ruthless"
First of all, Not true at all. He married her because she promised that she was gonna protect him. To stay by his side.
Look at it from his perspective, all he knew was that Haein gave up on that promise. Just imagine, one day your marriage is full of rainbows and as soon as you get back from work, the room that your baby was supposed to live in is being taken care of with no communication on Haein's part. It was a marriage but he felt like a slave.
"he couldn't see beyond his own bellybutton"
How do you expect a person to see another person's darkness when he himself is already shrouded by his own darkness.
Don't act like it was all Hyunwoo's fault when it's literally everyone's fault.
Again, the problem in the story was the LACK OF COMMUNICATION.