It's not on. Look, I'm OK with the fact that my hubby is still friends with a couple of exes - heck, I consider them personal friends of my own now. But they would never send him texts on a regular basis and they certainly wouldn't make overtures to him.
Thing is, she CAN choose to end this if she wants. A comment from her to them along the lines of "I'm in a relationship and you need to respect this. If you continue doing this, I will block you". That being said, I wouldn't be comfortable with having people around who need to be told this in the first place.
Anyway, she doesn't stop these guys because she doesn't want to. They are feeding her ego and she enjoys it. Frankly, I'd be moving on if I were you.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.