I saw the question you posted on my (very) old thread about what H did to make me think differently.
I get asked this question a lot because I was the person who ended it and then decided I wanted to work on it.
The longer I'm here I don't think there's any remedy or fix to every sitch. You can try to gain insight by reading what others have gone through but ultimately you have a find a truth inside yourself, that you will heal from this, that you are worthy of love, that the breakdown of you M was not totally your fault but also not none of your fault, so basically you each contributed, you can see your faults but not beat yourself with them, you can see her faults but not have any anger or resentment towards her because of them, you can let her live her life and make her choices without attempting to control or manipulate the sitch and you can love without any expectations of what the outcome may be.
This is what I'm struggling to do. We hope that we can learn to give love better and that by giving love better our WAS can see that we are now a more complete person and they've had the space without guilt to decide what is they want.
I had blinders on and felt like if we split up, if we D, if we moved on, if we found other people...we'd be happy. I wasn't happy in the M, I wasn't happy outside the M. And then suddenly my passive, needy, depressed, despondent, desperate H, treated me like an equal. He didn't look to me for validation. I now know it was because it got it from somewhere else, but I didn't know that. I had decided I had to end the M because he would never change he was happy like this. Then he became happier...he became more of the person I remember meeting.
He didn't find it from within so it's only temporary. He'll have to still do that work at some point. You find it within, you give her the space she needs to figure herself out, and you become a happier person.