Don't beat yourself up. Get back up, dust yourself off, and go back to NC. Sometimes it helps me to have a mantra when I'm feeling the way you describe. I try to repeat to myself "It doesn't matter, it doesn't matter, it doesn't matter." Nothing I say or do matters. It won't change anything.
Sometimes I just have to ride out the feelings and know I'm going to be miserable and uncomfortable a little while but the feelings will eventually pass.
Sharing any emotion with your ex isn't going to do anything except make you more upset...so it's like hitting your head against the wall. Eventually you will remember the feeling you get after you've done it. The problem is that when you are in a weak place and are feeling vulnerable, it doesn't matter how many times you hit your head...you want go through that wall again. You can say out loud...I'm not going to hit my head against the wall again. Lock in the way you feel right now after expressing yourself to her....try to remember that you aren't going to get the response you are looking for. It's not you....she just isn't capable of giving you and your kids what you need right now.
Have you read Codependent No More? It's a really good book. It's about letting go and stopping yourself from trying to fix things. I highly recommend it. I think for the stage where I am at right now...it really helped me to start detaching. You will be surprised at how easier it gets after a little while.
These feelings you are having are totally normal. The important thing to remember is that you are still capable of having a wonderful and fulfilling life without your ex. Your kids need you to be strong and healthy...and this isn't making you strong or healthy.
NC (except for kids and finances) helps you clear your head and get to more level ground. You will still have bad days and you will still feel like you are on a roller coaster, but the more consistent you are about NC...the easier it gets and the roller coaster starts to slow down.
It's not a game, it's your life. But ultimately you are only in control of your choices and actions.Once you get that feeling of control back...it's really hard to give it up. You can do this!