The best thing is to sever, and move on.
I think that, even if we published, got sales, met up, and got along, and put aside our childish misunderstandings, it's not worth it.
Even if on angrypages.com/read/ the guy's book is there, it wouldn't help me, it would only help him.
And my yetzer hara, my evil inclination, is to go this way.
We don't need to help, or help him earn money, and we definitely don't want to have any meaningful working relationship with the guy.