You MUST NOT send the money back. You MUST NOT contact him again because you sent the last email.
I do hate Rule things, but one mustn't appear desperate (apparently)
I once had a date (all right one night stand) with someone and the next day wrote a great long letter about how cool I was with it and I didn't care if that was it etc, but I just wanted to know becuase I didn't want to be messed around...pages of it, popped it through said person's letter box, got back home and found them on the doorstep.
Made him promise to put said letter in bin without opening it - yeah, that was likely.
Moral: Rusheth Not.