I've had something similar to this happen to me multiple times in my life.  People take advantage of your generosity and good nature and once you have been burned by them you turn into someone that just doesn't trust anyone, even the people that you should.  

It's a shame that this happened to you man.  I immediately think of the times that i have been burned (although not in something as untraceable or irretrievable as BTC) but I feel your pain  :(