Yes, I think just go back to the restaurant and act like nothing happened is probably the best thing to do. 45 dollars is not a lot of money, but if you can not afford to lose it, it is probably not a good idea to lend it. Besides there are government programs to help people who are facing foreclosure, and the whole story sounds a bit fishy to me. What is he going to do after his night at the motel runs out? I just think it sounds a bit bizarre, and I am glad you went with your better judgment.
I'm probably the only sucker who would have given him the money, thankfully I seldom carry cash but he would have talked me into going to an ATM machine.