Why would someone throw away a loyal partner for someone clearly worse?

Two years ago, my ex-wife cheated on me with one of her coworkers. I’ve been with my current girlfriend for a year, loyal, loving, and better than my ex in every way, yet I still can’t get over it. The anger hits randomly.

I’m 6’3”, fit, and have been told I look like a model. I treated my ex with love, helped her family financially, and built multiple businesses. And she threw it all away for a guy who’s 5’2”, broke, can't hold a job, and knew she was married to me. He even had a baby with her before our divorce was finalized and showed up at the hearing.

While we were still together, she showed me a picture of him, laughing, “Look at this loser haha, he thinks he has a shot with me.” To say I was shocked he ended up being the guy she cheated with is an understatement.

Afterward, she stole money from me and threatened to have her ex-boyfriend, a gang member, come after me, and I never threatened her.

The worst part is realizing I was that wrong about someone’s character and that my chance to start a family may have been stolen, since I’m in my mid-30s. My whole idea of marriage is shattered, and I don’t think I’ll try it again. My current girlfriend is 38 and doesn’t want kids, otherwise I would definitely pursue that. I’m not willing to leave her either because the relationship is otherwise perfect.

Questions:

What kind of person destroys a loyal relationship for someone clearly worse?
What kind of guy willingly has a baby with a woman he knows is still married?
Has anyone else moved past something like this, or does it linger forever?

Why would someone throw away a loyal partner for someone clearly worse?
Post Opinion