I think u should keep the money and give it to him when he gets back. he could be testing u, although, I don't understand why he should result to such a means to test ur trustworthiness. When I think of it, it's kinda degrading. But all the same, keep the money and return it when he gets back, and after some time, calmly ask him why he had to do that and make him understand that you don't appreciate it, one bit.

the way I see it, what we call 'love at first sight' is actually 'attraction at first sight'. It is this attraction when acted upon and nurtured that eventually turns to love.