Don’t feel bad. I felt bad about the ex not seeing his sons and sent them to go and visit him when they were trying to tell me they hated him. He just used his contact with them to further abuse us. Your son will be much better of without him in his life. He can begin to heal as can you too.
If your ex is like mine, don’t think he will be sitting sad missing his son. He will most likely be out partying and enjoying himself free from responsibility. We make the mistake of projecting our normal caring, loving feelings onto them and forget they have no emotions.
I hope you and your son find peace and healing. XX