Nice game about my standard so I understood it well. The rot set in around move 11 I think with hindsight white should play 11)d4. The ending was a roller-coster for black after that.
12.Nd3 looks better than what was played (12.Bf4). If 12...0-0 13.Be3 holds, but Black has good chances with the B-pair on an open board despite his crummy pawn structure (which also gives his Rooks 2 semi-open files BTW). Your opponent fell behind in development in the opening and paid the price, but he could've defended better. Of course the fact that he didn't is his problem, not yours!