Can I Get My Money back?

So I gave my friend $600 for a trip we were going to take in a few months. I gave this to him a few months ago guaranteeing that I would be going on the trip. So today because of his friend I told him I am not going to go anymore, but he wont give me the money back because its already gone towards hotel payment and other expenses. I have no way to show that I gave him the money in his account so can I get my money back or is his reasons justifiable?