i think, yeah, Dean’s early relationship with Castiel was, from the beginning, very confusing for Dean? because his first instinct was to absolutely not trust him, to refuse his very existence before his eyes (how can he believe in an angel who saved him when he can’t believe himself deserving of saving?)—and yet his first instinct was also to trust him. He defers to Castiel almost immediately, he nicknames him quickly, which is a strategy to make him more relatable in Dean’s mind and reveals the amount of trust he’s already invested in him.
that condradiction then, i think manifests too in how Dean views Castiel saving him: on the one hand, i think he is resentful of it—he doesn’t think he deserves to be saved. but on the other hand, he can’t deny it either, he can’t deny that it brought him back to Sam, that it brought this angel into his life who will become the best friend he’s ever had, that as much as it brought on a burden of knowledge, it also brought on a relief, because as much as Cas’ relationship with him is confusing, Castiel provides a grounding and an emotional outlet for Dean that he gets from no other.
so it’s all a contradiction, and even 5 year later, Dean is still trying to reconcile Castiel’s relationship with him, because it fits into no existing category in Dean’s mind: he’s a friend, he’s family, but he’s also an angel who chose him over heaven, he’s also someone who chose to be his family when he wasn’t born into it, and how can Dean possibly understand how someone could chose him?
as Jensen says, Cas is Cas, and that’s pretty much the only succinct way to describe him.