If you were clear that you weren't interested in the concert, I don't think you should have to pay him back. I'd be nice about it, though, because he did buy it for you.
Top 9: Chess, King's Field 4, Radiata Stories, Romancing SaGa, A Link to the Past, Nethack, The Dark Spire, E.Y.E. Divine Cybermancy, Dark Souls 2