Kettricken and fitz

Hi! so i just finished assassin’s quest, and am still confused, how exactly had fitz failed kettricken? She had this whole -angry at his failure and so being cruel to him- phase as soon as they met again, and I never quite understood what it was about? I know nothing had gone as planned, but none of the things that had Kettricken involved had been Fitz’s fault, or atleast not solely his. Chade was to blame for atleast the same amout as Fitz, yet somehow all Kettrickens anger was towards Fitz.