How 1200 crushed 1800

I played against a 1800+ a blitz game and crushed him completely though he was having one moment where he can equalize where I blundered but It is my best game till now.

Opening Phase
In the opening, at move 2 he played Ne2. Apparently this is called Alapin opening which I don't know to play against, so I simply stick to the basics and developed my pieces and was planning to create some attack on kings side as my pieces were better place I thought.

Middle Game phase 

At move 13, I played Nh5 because i thought knight is better placed there and some tactics could arise which later in game it did. Move 14 I played f5? I know that this is a mistake as my king is becoming week and the position would become bad in long run but also it is blitz and I want to go all in. He played h3? which turned out to be mistake. as i thought i was winning a piece by bxe2 as it cant take with Queen because Nxg3 would win which happened in the game and Nh5 became useful. but I was wrong after bxe2 there is a sequence of only moves by which white can retake the piece and it was too difficult to find I believe.

the answer is 16. Rxf5 Nxg3 17. Rxf8+ Qxf8 19.Bf2 and i won an exchange and slowly exchange pieces and setup and deadly final blow on the white king. so it is move 27 white played d4 which was a blunder find the move that wins for black.

it is bh2+ and eventually in few moves the white king got annihilated