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Nothing happens, just give back the money.
Come on mate, you are not in a relationship with someone? while each other sometimes mostly man sometimes provided their girl with at least transfer them money without reason to just make them happy (like buying food, or other).
Like I said, If you don't have any control then you are making your self trouble.
-snip-
Bitcointalk only Signature Campaign, they have their own forum discussion. Check on there.