Plot Twist Game

In my recent game against a 1914 rated player (arond 300 more than my rating) I was playing with Black.

I was going for the Elephant Gambit, of course, but on move 3 he played Nc3, so I just took some space with 3.d4. Everything was great until move 18.

On move 18 I was being defensive and I made a mistake, and from that moment my opponent was dominating the game. He was crushing me entirely with numerous opportunities for mate (M1, M2, M3, M4, M5...).

The Game: https://www.chess.com/game/live/101714541099

I am glad I didn't resign.