By getting out fast it seems clear it worked in your favour. Unfortunately you will just have to think of this as a learning experience.
As sad as it was to read what happened to you, by the sounds of it you could have ended up losing so much more than $600 and you always have your services on offer therefore you will hopefully generate new business and will be able to move on from the loss.
He asked me to promote his site. I said no few times.
Then he started to write in my native language. And he talked me into help.
First task was to give feedback on the site. In retrospective thinking that task was to pay me very little so I as thinking he was good guy ;-)
Then I should promote. I have my own system for that. But he talked me into using bitmedia. The amounts got wilder and wilder. 10000$ he asked for one day. And many other things. Every day some friendly message and some request for money. The classic I am out. Could you transfor for me and get money when I home. And different things.
I ended up losing 600$, Some will say that is wild. But I could have lost so much more. But I got out fast.