Black resigned.

For a successful attack, White needs to open lines on the kingside. For the sake of this, he sacrifices a bishop:

Not only attractive, but effective. 18.g6 would keep a strong initiative, but allows Black, after 18...h6, or 18...fxg6 19.hxg6 h6, to somewhat fortify the approaches to his king.

19...fxg6 20.Nxe4 dxe4 21.Ng5++–.

20...Qxe4 21.gxf7+ Kxf7 22.Ng5++–.

Other moves also lose:
A) 21...exf3 22.gxf7+ Qxf7 23.hxg7!;
B) 21...fxg6 22.Nh4! g5 23.h7+ Kf7 24.Nf5 Qe6 25.Rxg5 g6 26.Rh6+–;
C) 21...f5 22.Qxc4+ Qe6 23.Qxe6+ Rxe6 24.Ng5 Rf6 25.Nf7 gxh6 26.Rxh6+–.

Black resigned.

Bringing the passive knight into the game.

White had to cover the d4-square: 18.Nb1! Nd4 19.Bxd4 cxd4 20.Qd3 a6 21.a4 Qe5 22.Nd2 b5 23.g3∞.

White had evidently overlooked that after 19.Nxb5 fxg2! 20.Rxf8+ Rxf8, he cannot save the knight on b5: 21.Nc3? Bh3–+.