It's not sad - it's very human to hope for/wish for/want things to get back to normal.
I could feed you a line, and say 'give him time - he'll come to his senses', but the honest truth is this:
No matter what you do or don't do, he'll carry on with his current course of action (which you don't need me to tell you is selfish and destructive). He seems to be getting something out of keeping you off balance, which is unpleasant. This isn't about anything that you've done - it's all about him.
Now there are much wiser minds than me on this board, but in my very humble opinion you really need to focus on yourself for a while. You need looking after for a while, not him. You have DCs who will need you happy, healthy and positive again, not just putting on a brave face, so take this time to really care about yourself.
Be prepared though - chances are when you start feeling stronger/happier, your ex will start sniffing around again. Hopefully by that time you will be the one to have come to your senses though, and you will see that you are stronger without him than with him. Remember, you are in control here, not him.