Well, to offer a simplified but accurate assessment, Black lost because he didn't see a tactic.
Castling 0-0-0 with the half-open b-file is silly in the first place, and I think a lot of Black's issues come from his fundamental lack of anywhere safe to put the king. White isn't a ton better off, and both of you played a "wall of pawns" type of thing and trade off a ton of pieces before your development was completed.
The h6 and g5 moves are almost never worthwhile, and have the effect only of destroying your kingside. Before 0-0-0 White is thinking "Okay this guy's king is stuck in the center, so I'll put my rooks and Queen in the middle and crank open the pawns." Lo and behold, he doesn't even need to do that.
So I'm not even offereing a tactical move-by-move analysis here - this is strategic stuff where I look through the game and say to myself "why the hell is he doing that instead of getting his king safe?" I see no overall plan, no particular execution of a strategic idea or goal. You trade Bishop for knight early, part of the possibilities of the Nimzo-Indian, and gain what by it? What's next? Nothing. Nc6. Okay. Then g5, and after that, as of about move 9, as white, I'm licking my chops here thinking "This guy just tore up his kingside, maybe he'll trade out my bishop, but I don't really care because he has nowhere for his king to hide now." In the game white trades off your c-knight for reasons unknown, wasting two tempi to do so instead of putting his light bishop somewhere useful.
As of move 16 or so we are seeing that white has open attacking lanes, black is ponderously completing a pawn rush that it turns out he has no time for, and the game is done.
Moral: Develop your pieces rather than your pawns. Don't run one guy up the board and trade him off for no reason. Get your king safe. After this stuff, find something to do.
A carefully selected game that I played that needs analysis. I´m playing black. I lost this game. Analysis from both white and black´s prospective are welcome.