Where did I go wrong?
Sort:
I focused on the endgame, because I didnt see very serious, clear mistakes in the middlegame. I needed to use Stockfish, I'm not nearly strong enough at endgames without painful analysis. Turns out there are a ton of mistakes in the rook and pawn endgame. Unless your willing to do a ton of work to learn from this, I think the main take away is that you didnt see 45. f6 coming, and you can learn to do so. My guess is you probably had an "oh shit" moment when 45. f6 was played - I know I did when I was going over your game fast. There are no penetration squares on the queenside, so if you can stabilize things on the kingside rather than play b4 right away, you should have a very clear win. I thought, and Stockfish thinks, that 43. . . . pxp, followed by 44 . . .kc6 is cleaner.
Like I said, its all very complicated, and 43. . . . b4 doesnt throw away the win. The trick is that you actually cant play 44. ... cxb4 -- this is, oddly, the move that throws away a win. Instead d6xc5 is required, with the sae idea -- making sure the passer occurs more centrally, closer to your king, and after pxp, you play pxp and the position is won, although still not simple. Thats all rather counter-intuitive computer type play to me, so I think the thing to learn from here is to watch for the creation of a distal passer by something like 45. f6.
There are a lot of mistakes by both sides thereafter, and if you really work at it, I'm sure there is tons more to learn here.
Yeah, 0-0 is inconsistent. Have to ask yourself where your play comes from. h4-h5 (like most pawns moves) do two things: gain space, and weaken the pawn / squares left behind.
In other words, white's play is on the kingside. 0-0 does two things. First, now kingside play is quite risky, so you deaden your prospects and more or less consign yourself to passive defense. Second, h5 (and the kingside in general) is at a disadvantage in practically every endgame.
Almost always white will want to 0-0-0 in this kind of caro.
I actually stopped looking at the game there, and seeing as how oogiboogie gave a lot of comments (I'm glad he mentions 0-0), I'll leave it at that :)