You've had good advice on here, you really need to take control now.
I've been where you are now. It stinks. But please listen to me, because I want to help you so much.
You are still seeing all this from his perspective; like saying "he'll be cross" up thread; so bloody what! It doesn't matter what he is, or says or thinks any more. And that's a huge thing to come to terms with I know, but regardless of whether he's 'cross' or not, you should be bloody furious! And you're not - because he has done a huge number on you, and you have (like I did) taken all the responsibility for his happiness, and the downfall of the marriage. This has to stop. It will take a while, because he's further down the line than you are: he's already checked out of the marriage, and you're left playing catch up. Well, you need to catch up fast.
Right now, you're desperately clutching at straws, and trying all you can to try and make this right. You can't. So stop trying. Stop wasting precious energy and emotions on trying to fix this. He broke it. Not you. This is him. He has thought this through and deliberated on this for a long, long time.
He has told you he wants out. When I was told the same, my whole world broke into a million pieces, but guess what? I took control, and started to heal. You really don't need to see phone bills, FB messages and all that shit. You just need to focus on YOU. And kick him out.
Tell him he has to leave today. Where he goes, what emotional baggage and history he takes with him, is his problem.
Get strong, take control, and KICK HIM OUT. Please - for your sake and your kids. Because if you don't, you'll spend the next few months trying to fix the unfixable - and it's not you who can fix this. Only he can fix this, and he doesn't want to. Sorry, it's lousy and sad and seems the end of the world. But you will get better, you will get over this. But you need to take control to do so.
I wish you all the luck in the world. X