You can thank Messi also, not showing up for what was arguably the most important match, let's also mention how horrible he played against Milan..
It's the tactics that have failed the club this season in their biggest matches.
Messi is the only goal threat and he's playing too deep right now and is getting swarmed by opposing defenses the moment he gets the ball because a player like David Villa or Eto'o isn't out there and opponents know it.
The team has never been strong defensively but if they want to go the full-route of having Iniesta on the wing like he does for La Roja, then Tito and Roura should have put Busquets-Song as a double-pivot just like Del Bosque does for La Roja with Busquets-Alonso. Barca would be much stronger defensively for it. A 4-2-3-1 would be the best formation right now, Messi should be the one moved to the wing and let Villa play as a CF.
They have to fire Tito Vilanova and his staff, bring in somebody new with new ideas. I have a hard time believing Pep would have threw this lineup out there.