Horrible Ex

What do you do when you honestly cannot make decisions and coparent with your ex? My son's dad is the most selfish person. I'm not perfect, but 9 time out of 10 it's because I've reached my breaking point with the BS he creates. I bend over backwards because I think not fighting is what's best for our 7 year old son, but it's never enough. He bullies and yells and threatens until I give him his way, but he almost never compromises in return. I don't mind if it really works out for our child, but sometimes it doesn't. It's so hard to sit back and be a part of a situation I know is detrimental to our son and feel powerless to stop it. We have 50/50 custody. Our son had had quite a few discipline problems over the years, both the school and myself have tried to get counseling for him, but his dad refuses. His dad constantly talks bad about me to and in front of our son.  I consistently give up my time so that our son can do "special" things with his dad's family, but he won't do the same if I have something on his time or he'll use it as an opportunity to extort something from me like giving up a holiday or an extraordinary amount of my time. He lets our sons insurance lapse and lies about it, so now I'm going to pay for his insurance even though our paperwork says he's responsible. I'm afraid to take him to court, because I know that he'll find a way to retaliate even if it hurts our son. Plus the all the money and fighting that goes into court is terrible.  I just want my son to be happy and for things to be fair. I don't mind compromising, but it's never enough. What am I supposed to do?!!!