"The big bad is back, and you will aaaggggg"
- Jul 31, 2018
No, it was Warren's fault, only Warren's fault. Xander was kinda shocked when he saw Warren in Seeing red. He didn't react at the gun that Warren pointed at Buffy. So after that he feels kinda responsible to have not do anything in that moment like he's asking himself "what if he reacted at that moment, he could have stop Warren". And I'm sure he feels bad for that because earlier in S6 he left Anya and hurt her badly. He feels like a loser, he is even angry at himself in the beginning of Two To Go because he feels useless to help Willow, his best friend.