you already knew the answer:

"I guess the best thing for me to do is to break up with him and move on with my own life,"

You were wrong at the beginning. When a man is still in a marriage but started chasing other women, it shows his character.

You don't have time to give him chances to return to you since you are a middle-aged woman. I don't think he will ever change. Don't waste your time on him and move on.