Honestly? I think you're still being incredibly naive.
King pin dealers (as you've described him) might get clean. They never get out of the industry. They stay in it for life, go to prison or die.
You think a king pin drug dealer is going to... what? What job do you think he's going to do? He's no actual work experience and would need to leave every friend, relocate and take an entry level job (depending on what he could get with his prior convictions) for say £18k. You think a man who is used to unlimited funds is going to do that? You need to catch yourself on and be realistic now. It's ludicrous to think he would do that!
And I'm worried you're basing your decision on him getting clean. Even if he's clean, he is not going to stop being a dealer. I think you know that deep down and are still thinking that if he's clean then you can turn a blind eye to the dealing. Which, by the way, funds organised crime, prostitution, trafficking... a plethora of disgusting things.
If I was you I would take advantage of the fact he will want his chosen 'career' and lifestyle more than he wants you and your son and will allow you to just cut contact if you don't report him to police.
I would be tempted to cut contact and move away so you can get on with your life. For the safety of your child.