I can completely understand. I've gone back and forth on feeling sorry for AXH (he's missing out on so much) - hating him - just being angry at him... The feelings are just feelings. They aren't wrong or right; they just are. Eventually they pass, or change, or recede into the background.
Whenever I get to thinking AXH is missing out on so many wonderful things, I remind myself that I'm basing that sadness on how _I_ would feel. It doesn't mean that AXH feels the same way.
AXH had a lot of potential. He's really good at things he sets his mind to: rugby, rebuilding motorcycles or cars, underwater welding. He could have been a great sports physio if he set his mind to it; he had the practical knowledge and looked at going back to school... But the short of it is, he didn't keep up with any of that. Which is unfortunate, but nothing I can change. And to quote Margaret Atwood in Cat's Eye, "Potential has a shelf life."
And honestly, when the sadness-for-the-mess-he-made funk starts kicking in, I log into the child support services account and look at that unpaid balance or go peek at his FB page and see the photos of his new motorcycle or pics of him and his current GF at a pub and just like magic, that sadness changes yet again.
One of these days, I may reach what I see as the pinnacle of getting past him: indifference. I'm not there yet, but I get stretches of that the longer I'm away from him. Sending hugs for you and your kiddos.