The problem with this side variation, as is usual with deviations from theoretical main lines, is not that it's losing; it's simply not best. In this particular case, it doesn't develop a piece (unlike the main line 6...Re8) and limits Black's mobility in the center and with his dark-square bishop. White makes obvious moves to take advantage of this, kicking Black's bishop back to b6 and then developing with a threat to the kingside with Bd3. At this point, though, White - perhaps focusing too much on the 100-point rating gap in Black's favor - opts for a weak plan of simply trading minor pieces. By move 12, White has negated any opening advantage he had, allowing Black to pass him in development and also handing Black the initiative with threats down the c-fiile.
Black for a time presses his initiative well, but then lets up for one move and White is able to almost equalize again. Unable to make progress, Black trades down and enters a Q+2R late middlegame/endgame which White should be able to hold with little difficulty. Unfortunately, after 32 moves of hard-fought battle and feeling the pressure, White fails to fully calculate his 33rd move, again focusing on the illusory simplification of the piece trade and not its consequences. Black then penetrates with his queen and it's all over.
Although analysis shows some of my play to have been erroneous or not optimal before the final error, the game was at least a worthy struggle. The problem at the end was can be ascribed to laziness (or tiredness, more charitably). I've seen this happen before in my games, including more recently, and it remains an object lesson. A chessplayer needs to have the mental capacity of a marathon runner, treating all moves until the end of the game as important. Just as importantly, a player needs to have the energy to tackle them appropriately. Sprinting is good for as long as it lasts, but most games are going to go the distance.