Social services and my grandparents removed me, and my siblings, from my parents. I wanted my parents back desperately.
I was 7. I didn't know that the emotional, and physical, abuse we were getting wasn't right. I just wanted the safe (ha!) life that I had always know.
I will be FOREVER grateful that the adults around me realised that being a child I simply didn't know what was best for me.
It took a long time and a lot of work, but eventually, when I realised that the home that I lived in was a safe place where I was never going to be bullied or belittled or hurt for making a mistake; and that my Gran shouting at me for playing by the river was because I was in the wrong and she was scared, was amazing. Honestly amazing.
Please, please do not take an abusive, bullying man back into your life because your 8 year old thinks that is what he wants.
He thinks he wants that because his Dad has made him, and possibly you, think that is normal. Your son needs re-educating and stability. He doesn't need a Dad who treated him, and you, so badly that you felt the need to tell him to leave in the first place.
There is no easy route to helping your son through a tough time. Taking his Dad back certainly isn't an easy route.