so sorry you are going through this...
I can only offer that I've been through a similar ordeal. My ex was my very best friend, he was the only one I felt who understood me, and we did everything together. When he decided he didn't love me anymore and that he needed to lvie his life, I was beyond heartbroken. I went through a depression, felt awful, couldn't eat/ sleep, spent tons of time and energy trying to get him to see the mistake he was making. For a long time, I couldn't keep myself from calling him, even if it was to argue. I actually would pick up my phone in secret and spend huge amounts of time talking and crying. I didn't undertsnad why he was leaving me, what I did wrong, how things could be better or be fized. Until at some point, with a lot of self discovery and therapy and tons of support, it turned into anger. I was furious, angry, and hurt. I knew I didnt' deserve what had happened. It then became acceptance, and took me realizing, eventually, that I was so much happier in my situation. Is it harder? Yes! Is it lonely at times? Yes! Would I ever trade it back to have what I had before? Never. Do I love where I'm at now? Absolutely. I learned so much about myself, about my dependencies, on my self esteem and worth, and how I didn't value myself. And although I'm still working on things 2 years later, I have become a much stronger, independent, happier person through a lot of work.
I guess my point in all this blabbering is that I thought it might help to know others have gone through similar situations. It took me months to be okay with things. I tried so hard to push him to see the kids, to stay close friends, so understand and be there. And now we actually do get along and can have a wonderful divorced relationship, but I had to separate myself from my husband, and really put it back to him being my "ex". It's so difficult when there's kids, because you may end up having to have a relationship with your ex for a lifetime. There's even times now when he pushes for us to all be together for lunch or an outing, and I have to say no because it's too much for me, and doesnt feel right. Other times, things are fine. I have to figure out where I draw my line, which is much different than his. There are certain things that I know I shouldn't do, or that in my mind, aren't ok. And then there's others that are fine for me, but others might not understand it. It's just a huge learning experience.
It is great if you can pick up the phone and talk to someone else when you feell like talking to him... I think that would have helped me a lot at the time. Same with him visiting or me coming up with excuses to see him... I've done that too. :P And going out and having a distraction. I stayed home a lot and it really heightened my depression at the time. Moping at home alone was awful.
(I hope that made sense, I'm tired so I can't tell if it does