A few years ago I had an exclusively online friend, we fell out (over something trivial, not money in this case) he then sent me an abusive email. I was traumatised that someone who had never met me could be so mean, also ashamed that I had allowed myself to care, I was really upset and scared by the whole thing so understand what you mean.

It's not your fault this happened, learn from it and move on, in my case I decided never to make any more exclusively online friendships.