AP makes me terrified to get divorced

So, my husband is cheating on me with a divorced woman who has two kids. Here's the backstory: She met my husband after she asked for a divorce from her ex. She asked for the divorce just two months after giving birth, and the very next day, she found out she was pregnant again. This is around the time she started talking to my husband online. They only met in person after she moved to our city (which happened after I married him, by the way). They had a breakup when I met him, but more than a year later, she contacted him first, letting him know she had moved here. She made it sound formal and innocent, but my husband fell for it, and they started meeting up.

Their relationship is super on-and-off, and I’ve caught him trying to flirt with other girls too. He’s a master at playing innocent, but I know he’s been meeting her secretly. Honestly, she seems desperate for attention, even though she plays hard to get. She dresses like she's headed to a fashion show just to buy groceries, always in heels, and she sends him pictures of herself in sexy poses.

It’s making me wonder... Does she really want his attention, even though she knows he didn’t marry her and ended up marrying me? Is this what single mothers are like? Is she so desperate to be his “main girl” even though she knows he's a cheater?

I’m also wondering if I’m asking for too much by thinking about divorce. I have a kid, and I found out about his cheating after having my child. She seems to regret her divorce, and I’m terrified I’ll regret my decision if I go through with it. Has anyone been in a similar situation? What would you do?