Letter is good. I think I would take some of your ( I feel) emotion out of it. "I'm concerned he won't have a relationship with his father" kind of stuff. Leave that to Dad. Just stick with the facts. Is your son's counselor able to back up your feelings? Is he/she concerned about how child acts? Ask your counselor to talk to your child about how he feels when Dad gets angry and see if counselor will back you up. Your oldest is a teen, correct? Will he go in front of a judge and tell about Dad's behavior? Start documentation on how your child is when he comes home from Dad's house. Best of Luck your ex sounds like an ass.