Backed into a corner

In this game, correct me if I am wrong, but the person playing white castling seemed to hurt him more than help him in the position he was in.  Once he stepped up his pawn to stop my queen-rook attack, he left an opening for my knight to fork the queen and king. Once I saw that the bishop could scare off the white rook protecting his pawn from my knight, Checkmate seemed eminent.  One question though, even after I moved the knight to a better position, what would of been the best move to stop checkmate? It just seems that sometimes castling puts a player in a worse position and easier to corner.  Any insights or comment are very appreciated.