What do I do with him?

He's an adult, in age if not in actions. I can see that you have good intentions in wanting to help him but I doubt it will in the long run. If you were to set up a private arrangement then firstly I doubt the fraud investigation would stop and also what would you do if he defaulted on your private arrangement? I think you'd be best sticking with the CSA, yes they've got their faults but at least it would save you the hle should a private arrangement breakdown. As far as seeing your child, well there isn't much you can do about that, it's very sad but perhaps your child is better off without him in their life. Maybe in time they can build a relationship. Best of luck x