I think 3.Rh1 is the problem move. Fritz 13 says its white best move but I think white can avoid my fortress by just moving the rook aways from c1 before going to h1.
My, I think, drawing end game idea

Computers are bad at this stuff because of how many moves in the future it has to go. I think I can win this against you from the final position (almost a fortress).
Here it is in words: White walks his king to c6. This freezes the black bishop on c5 (must guard both pawns). 2. The white rook works over to the f file and helps the pawn move to f4 and trade, either way is fine you capture or he captures. 3. sac rook for bishop from the side. 4. Munch pawns with king.
The only tries for black to stop this are walking his king to the b file, but then the white rook cuts him out of the game from f7 and Rf5 forces the king away from the f4 square.
Heres a picture.
I found myself in a pretty tight spot but managed to build a fortress. My opponent didn't manage to crack it and fritz couldn't either... but fritz is notoriously bad at end games.