Sometimes it feels like on a subconscious level, when they don’t even know they’re doing it, Dean and Cas have a type.
A+ casting
Dean imagines a devil with dark hair and blue eyes (and angel right after, btw, so that they’re kissing and distinguishing one from the other is almost impossible): a fantasy that is meant to be kept private. We don’t see Dean getting with a lot of girls that look like the above. And yet, as Anna says, “This is what you dream about.” Front and center in Dean’s dreams is a devil with blue eyes, dark hair – no, that’s wrong, angel. Feminine, blonde, has to be long blonde hair, not short and dark like a man – the second girl is almost an autocorrective impulse.
For him, this Type is Something He Can’t Have, so he doesn’t go after it. Even when it’s right in front of his nose.
Same for Castiel. Daphne, a wife with green eyes and soft brown/auburn hair that takes him into her home without any questions asked, is not something that’s available as long as he stays who he undeniably is. Castiel has to change himself, give up huge parts of himself, in order to remain with her. And he does sacrifice that happy life he has with her in order to do what he was always meant to: smite demons, help the Winchesters, be righteous and holy and unbreakable again.
As long as Castiel remembers who he is, this Type is Something He Can’t Have, so he doesn’t go after it. Even when it’s right in front of his nose.
Both of them think that it’s impossible to get a firm hold on their Type in the real world. Which is why they’ll always be confined to dreams, never acted upon, always subconsciously played out across our screens in the most frustrating ways imaginable.