Please Help Me Analyze My Game

Seems as though, just at first glance, you took a little too long to get your king involved, either by disrupting his pawns or protecting your passers.

I think the main opportunity I missed was 36. Ke5 instead of Kc5

I say that move 30. cxd5. Then you would have had your rook to defend the promotion of his pawns. You were a little too eager to trade, but you need some peices for the end game. What will you mate him with if you have no peices. You guys were dead even at this point. Maybe you could have got you king over to play defense too. If you opponent was slipping on move 30 & took your pawn, you would have the upper hand...

I agree. Right there you went from a roughly equal position to a lost one (at least against a player with a 2000+ rating). That's a pity. You didn't play your rating till then.

42. Kb6 is better than Kd6

Maybe, but it doesn't save the game either.

You have played quite a decent game there, my congrats! You certainly show some potential.

I think the most important things have been already mentioned: 20.Bxb4 drops a pawn and so makes your game difficult, on the other hand I doubt that the rook ending after 30.cxd5 is better than the pawn ending, which with correct play should have been drawn, not lost.

The actual losing move was 36.Kc5??, which sets the black e-pawn free. Instead, 36.Ke3 draws, because your pawns protect each other just as well as his: 36...Kb6 37.d6, and his only move will be Kb7, either immediately or after moving his h-pawn. Similarly you can react to 36...Kd6 with 37.b6, although there you have the additional possibility of playing 37.Kd4. The interpolation of h7-h6 and h4-h5 at some point is not going to change anything significant.