Stalemate occurs when a player's King is not in check, but any move by any of the pieces would put that King in check. Quite simply, White had no legal moves in the position, but he was not in check. Your Queen guarded all the squares on the f-file, your Rook took away all of his options on the h-file, and your Bishop prevented him from moving his King to g5. With his Pawn occupying g3, he had no legal moves to make. Since you also weren't directly attacking his King, it wasn't checkmate.
The result of these factors is that the game is drawn by stalemate. Sadly, if you had played 43. ... Qe4#, instead of 43. ... Qxf8, you would have checkmated him and won the game. I hope this explanation helps! 
i had a 6 to 2 advantage over cyrano8 and 2:54 left with opportunity 4 more queens,i dont understand and any help would really be appreciated thans much richard gruis