My counsellor gave me "the leaver and the left" information to try and explain why he was so much further down the road than me, and why he didn't give a damn basically.
My XH turned into a complete stranger, he changed from the loving family man, into a cold hearted person who said some horrible things about me. He had no idea what he did to me, or how much he destroyed me. This man had loved me for 10 years. I still loved him very much at the time and begged him to stay.
XH left with no warning, blaming me for everything, so of course I tore myself apart. However, counselling helped me to "own" the flaws that I do have, and throw away the shit that he said about me that was destroying me. It also helped me to see his flaws, and that I didn't need to accept responsibility for his actions and his decisions, he is responsible for those himself.
The more civil you can be with your XW , the better it will be for the DC, but it is very hard. My XH did not understand the level of hurt and grief that I was suffering and I couldn't see him at all. He then got nasty about a lot of stuff and now we barely communicate and he chooses to see DC as and when it suits him. That's why I say, be a good dad, because it is only the children that will suffer, not your XW, if you mess them around.
I would go to the doctor if you feel low as they will help you. I was on anti depressants for over a year, but it got me through the divorce and counselling.
Exercise is good too, so keep up with the cycling. Are there any cycling groups locally that you could join? It sounds like you have very supportive friends and family too, so that is good.