chess online

if white moved Ne5, black would move Qxg2# for mate. Presumably, that's why black moved the Queen there, but black overlooked a crucial move (white Bb5), so that's really a blunder.

The reason for the Bb5 move is as follows: first of all the bishop is backed up by white's queen so black can't simply take. black must find a square to move to, but all possible squares are covered.

If:
Qxb5 Qxb5 (or Nxb5)

If:
Qxc5 dxc5

If:
Qd5 Nxd5

If:
Qd6 cxd6

If:
Qe4 Nxe4

...so black goes down swinging and takes the knight for some compensation. Hopefully I didn't miss any.