This game looks very odd, wich makes me hard to believe that your opponent was really rated 1820. Also I can't believe your rating is 1550.
move 10:
Easy to win a piece there. Nxd5.
It's weird because later on the piece is getting captured anyway, by bad play of your opponent.
On to move 19:
f6!!! It would have equalized the game because if you pull away the knight then Qh6 (the quiet move) gives checkmate next move. I find it hard to believe that a 1800 player didn't find this.
19...Rh8??
You say it's the best defence there is. I say the best defence is simply f6 and g5 on the next move.
20...Ng8. What's wrong with this move. The kings house is getting an extra piece to defend. he can play rf3 anyway no matter where you put the knight. At this point you were seeing ghosts.
Then on move 29 you had failed to see the mate in 1. Qh3# wich right away gives me my conclusion: You are not a 1500 player.
Nevertheless, you played okay! Understand that I'm trying to help you and not burning you down. Goodluck in the rest of your games.
Played against one of my regular club members in Toronto: