It's easier to get help if you post the game.
One problem that plagued you is that you couldn't castle. 8 Kf1 wasn't good,
You should have interposed with the b knight or the bishop.
With 9 a3, you missed your first chance to win a piece but you eventually saw it.
With 19 Nxg4, you were up by two pieces. Unfortunately, your king wasn't safe because of 8 Kf1 and your problems began.
20 Be2 made the problem worse and after he piled up on it, you lost a piece with f3.
Another 10 moves trying to untangle that situation and you lost the exchange to a fork.
You ended up in a difficult two piece and four pawns against rook and six pawns endgame.
The computer says you were worse but had a chance to draw if you had cornered his rook with 42 Nd2.
https://www.chess.com/analysis/game/live/92400753915?tab=review
Someone can help me to analyze this game? Except for the obvious bad mistake of the fork, what other problems do you see in this game?