A sure win. Or is it?

Here's the end of a game I played with a friend.  This sequence begins at a point where the situation looks pretty locked and my opponent offered a draw.  However, I spent a lot of time thinking about it and working it out on the analyzer option during the game and believed I had the advantage, so I declined the draw offer.  When working it out ahead of time, I couldn't realize all the ways my opponent would be able to fight back or how close I would come to queening the b-pawn, but it still worked out in the end like I visualized it.

No matter how I worked it out ahead of time, I couldn't see a way for white to get ahead and win.  Can you?

thanks, tonydal!  i really appreciate your input, i really should play more decisively, not waste so many defensive preparatory moves.

Your king should move foreward to support your passed pawn(b5), and black's rook will be free to attack and to advance foreward.