do you think that castiel had always in his mind to not honour his contract with crowley?

For me yes...maybe it's the reason for what he asked to dean to trust him, said to him that he knew what he's doing..he knew that he never honour his contract with crowley just using him to have the key to the purgatory and that the major reason that cass didn't want to see crowley after the boys, his real family
he never said the "real" true to dean because he knew that crowley had spy everywhere listening everything and certainly that dean didn't accepted that...he was sure that dean gonna trust him and didn't believe that dean didn't do it...in his mind, that was clear because the boys and bobby were his friends and must trusting him after all they lived together...and this miss of trust confused castiel...and making doing the wrong choice because he didn't understand why...didn't understand that this pact was a treason for dean who lost so much because demons things...it was a too hard lesson for an angel who learned to be "human/angel" free