Gabriel wasn't sure why the boys put him, out of all people, in charge of you. He was the most irresponsible one out of all of them, yet he was left in charge of a kid. You were Castiel’s host’s kid, Claire’s sibling. While Claire was fine staying with Jody, you ran away from her house so many times Castiel just made you stay with him. Over time, his care turned from guilt-driven to just care-driven, and a real bond formed. That didn’t mean he still trusted you to be alone.

With all of this portal stuff, everyone was busy. Sam and Dean on a lead, and Castiel was trying to find Jack, it just left Gabriel and you alone in the bunker.