Some people are not right for each other
I know you are struggling right now but I want to let you know that leaving him was the best thing you could have done. The reason you feel so unsure is because you are deep in a bad case of postnatal depression and so feel totally unsteady, but it is the best thing for you both and the kids to be apart from each other.
Some people are not right for each other, you may have thought you were but actually you brought out the worst in each other.
The girls will be okay, the older two especially as they have their own Dad and your baby is still a baby, she wont know any different and eventually you will be in a place where the two of are able to co-parent (it seems impossible to understand but I am telling you, you will get there).
Feeling guilty about the effects on the children is not going to change the situation, and keeping them in such a volatile environment would have been something you would have felt far worse about.
Now what you need to do is look after yourself, a break up and such severe depression is enough to crumble anyone, but you won’t crack, you are stronger than you think. You have proven this by leaving. You should be feeling like Thelma and Louise right now, though I know the drugs probably won’t allow such emotion.
You will feel better soon, you have a great family to support you and a wonderful mental health team in place, you are stable, you are strong.
I know you cry at nights, I know you feel like you have failed and I know that you want to turn back the clock, but to where? If you had never met him, you would never have had your baby girl, so for that this part of your life journey has been essential. I know it’s been tough after having her, and I know you have been on your own coping with it, but now you are free of feeling ashamed of getting PND again, now you won’t be berated for crying and now you don't need to made to feel like the whole thing is just attention seeking, it’s not a joke and I know you don’t want the curse of depression around your neck. The doctors understand and they will help you through this, as well as everyone else.
The crying doesn't need to stop but the laughter does need to grow, you are funny and bright and full of life and your girls need that back. You have everything in place now to become you again, the restraints of depression will be aided by the magic pills and the restraints of a controlling relationship have been cut. You are free.
So though I know mother guilt stays with you, I want you to know that leaving him was a good thing for you all, it will allow both you and him to find yourselves again and it will allow your children to see the best of you (something they have missed).
One day you will look back and see how this was a turning point in your life, you will be able to be civil to each other and I know you will both be grateful that you created such a beautiful human being together.
From this you will both learn
You are strong
You are free
Now live for you and your girls,