1. ... Bh3
2. Bf3 Rc3! (Indeed, here we go! By the way you made a little typo: Bf2 ...)
3. Bxg2? Rg3 and black wins.

If white doesn't take g2, his position is worse, too:

1. ... Bh3
2. Bg6 Kd7
3. Bf5+ Bxf5
4. exf5 Rf8
5. Rxg2 Rxf5
6. Rd2 g4
   And black has a clear endgame advantage, because finally white must play Rg2 (or other rook maneuvers) to stop the black g-pawn, but then black will play Kxd6 and wins.