I think it's because he is on a different page. You are trying to be nice, be fair and put your childs best interests first. You perhaps have the same expectations of him. He doesn't share your beliefs. In his world he comes first and his mum might be the same.
My ex demanded I let him take dd to a cafe when she was 6 days old. I said no and so received the formal request from his lawyer when she was 8 days old. WTF?Of course this won't happen anytime soon. My dd is now 6 weeks old and FOB will come to see her, wake her up and he expects her to pay him attention. Why? Because its about him, his needs, his expectations. My beliefs are different and to get him to change this continual waking of dd I have to write a letter to his lawyer and stipulate this needs to change. Grrr. I find it easier to understand (I don't like it though) if I see his behaviour as selfishness.
I can empathise with you. Its hard work