This is uncannily similar to the way that things played out with myself and ExH. We had been together for 16 years, with a 5 & 3 year old, when I found out that he had been cheating on me. I didn't leave, for fear of the unknown. As the months and years rolled on, I uncovered even more infidelities. He never wanted to leave me, he wanted his cake and to eat it too.
Like you, I put up with so much crap, for fear of the unknown (he had been my first BF!). Anyway, after a few years, I started going out more, and one night in a nightclub, I was chatting to a lovely man, who suddenly kissed me! It was like a lightbulb moment of realisation, that I was attractive and that "other men were available" (Not that you need a man of course). Over the next few months, I completely switched off my H, and started seeing other men and plotting to leave. I did not get serious with the man from the club (we had a few dates), but he was the catalyst for change in me, and realising my self worth.
I moved out with the children (who were 11 & 9 by this point), and we got a lovely little house of our own. Naturally, at this point, ExH thought I was the best thing since sliced bread (eye roll) and begged me not to go. By this point I think I actively hated him for what he had done.
A few months after moving out, I joined a dating website and had a bit of fun. Then I met my now DH. He is so different from ExH. So caring and loyal, and decent. We have been together for almost 15 years now. When I think back to the amount of shit I put up with, with ExH, I can't believe A) that I did, and B) that he was such a bastard in the first place.
Also, I think it's worth noting that with ExH, he was given several chances to change, before I left him, but he never did. So even if you cave in now, he will revert to type. He also cheated on his partners who came along after me. And, I think he's currently cheating on his current long term partner who he lives with.
Not sure if my story helps you. But it seems just so similar to yours.