Eris isnt non trusted by cayde no more than cayde mis trusts ikora. Cayde doesnt really trust any one tho. But then he did tell holiday his plan before anyone else (even the guardian he was sending to do it) At end when eris was like My queen you were right the guardian was the key (Key to oryx's downfall in that case, the crystal from oryx blade is then used to craft swords for guardian)