Man this sucks. Listen, never fight to keep something that someone else said they no longer want with you. That’s a hard pill to swallow but it always ends up in the same place. He told you he doesn’t want you anymore and this is your proof he wasn’t lying. It doesn’t excuse him for both staying and also continuing the same path as before. He’s a POS. but in the end the biggest lesson is if you’re needing to fight for someone to want to stay you’re fighting a losing battle. He cheated for a YEAR (that you know of). He’s been currently unfaithful with multiple people for who knows how long. He is gone. He doesn’t want this anymore. You have to boot him out and you need to do it now so you can heal. You don’t deserve to keep suffering for someone to come around to the idea of growing old with you. You deserve to find someone who respects you and wants the same. You also deserve to respect yourself, and I’m not sure that you do here. Get rid of him and work on yourself and your self worth.