Sorry to hear this is happening again Sid when you were seemingly happy.
I think you need to search deep within yourself this time not just for you, who is falling apart over this situation but for your children that will be feeling like a yoyo in it all. They will not get off unscathed now or in the future with your indecision. It is something that is important enough that you have to make it once and for all and stick to it without waivering.
It might be the hardest thing you have had to do but you have done it once before and you were doing ok and you will find that peace again.
You are too good of a person to have to put yourself through this with someone that doesn't appreciate your worth and with that she is taking away your own confidence in yourself. This in itself is causing more personal damage to you, something you have been working so hard on!
People don't change Sid unless they want to change for themselves, you can't please her because she isn't happy with herself so she is finding fault in you.
Step out of the picture, look at this story as if it were another thread in here and you write your evaluation of the situation. I know what you would be telling this person to do...