You can do this, and you will. If it was not this woman it would be someone else, the man is incapable of staying faithful. Do you really want to live like that? Accepting some crumbs of comfort when he decides to be nice to you for five minutes?
It's just uncertainty and worry about the future that is making you upset, you have your friends and family around you, you have your sons support.
Yes, you're right he doesn't care, he's not the man you married, he's a selfish, insensitive bastard. But you can't change that, you can however change how you react to this going forward. You either stand or you fall. The best revenge is to live well. You will not be alone, eaten by cats, you will be a new woman, independent and living happily, maybe with another partner if that's what you want.
But for now, you are still grieving the future that you expected to have, it's very early days. You are still in shock I believe, the pain is still so raw for you. I'm holding your hand, hush my lovely, I've been there and have the particularly shitty t-shirt. It just takes time to get through this.