What now?

So this may be a little long,but I will try to keep it short. My husband and I have been together for 20 years and married for going on 8. We broke up about 11 years ago for a few months and both started seeing someone else. After a few mobths we knew it was wrong and decided to be together and end the other flings. I ended mine and thought he had also. But he apparently has been "talking" to thos woman who knows we are married on and off the whole time. I caught him once and he swore it was over and I tried to believe him and took him back. Fast forward to now and I find out he has recently had a full fledged affair with her to the point of telling her he loved her (which he says was a mistake and he never should have said it) and of course now he's saying he loves me and only wants me but then I find out he's still talking to her. Amidst all of this we found out my mom has stage 4 lung cancer and I'm freaking out about that and trying to help her get through this. I know I need to just walk away and let him go, but I just don't know how. With everything going on I feel like I need him now more than ever 😭😭💔