Before hand or when you gave him the money was there any kind of discussion about how and when the loan would be paid back? Was it documented? Did you give him a check or cash? If there's some kind of proof that you gave him the money as a loan they you at least have a legal path to take. However, if he has pissed the money away and there isn't much potential of future income then it may be fruitless to pursue.

Did you not know he was not motivated before you gave him the loan? Why did he need five grand all at once? Sounds like maybe you're as ticked with yourself as you are with him for allowing him to take advantage of you.