Hi op. You can't change him, only your response to him.
I'm just reading a great book called 'you can't ruin my day' by Allen Klein and this quote from there comes to mind:
'Your anger and resentment is completely legitimate but holding on to it is only holding you down and preventing you from moving forward. It zaps your energy - energy that you could use more productively to fully get pleasure from your relationships and enrich your life'
Your response will also affect how your children feel about things. Take the pandemic for example. I have friends whose kids were really anxious about it and upset at missing out on stuff. I was really relaxed and talked positively about the things that we could only do because we were in lockdown. My kids missed some stuff but we all had a relaxing and enjoyable time.
When I split up with my ex, he wanted 50/50. I didn't know if I could cope not seeing them all the time as I'd done all their care during their lives but I looked at the bright side and enjoy my free time. Equally, when I split up with my eldest's father, he never saw him so I had full custody of him. I was grateful that I didn't have to miss out on seeing him.
My ex financially abused me and left me in a very difficult financial state. It has taken me a few years to get to a place where I'm financially comfortable doing a job I love and I'm on target to make a considerable amount of money next year. Maybe if my ex had left me in a better financial state I wouldn't have had the need to look for ways I could grow my business and would have just coasted.
I see it with friends all the time. Their happiness isn't usually about their situation but about their outlook. There are things you can't change in all our lives, so we may as well look at the positives.
When I've felt angry or upset, I always think about how lucky I am to have my kids. That they are healthy etc.
Your ex is missing out on his kids. My ex wasn't around much when they were younger and didnt lift a finger. I was frazzled but it was him who missed out. He has them 50/50 now but they are older and busy doing their things.
All the best op.