This is the issue: Dean is not in love with Castiel, angel of the lord.
If Dean were in love with Castiel, angel of the lord, that might not be that big of a deal. Because it’s a freaking angel, okay, it’s celestial energy funneled into a vessel that just may happen to be male, sure, but that’s not what counts, what counts is that it’s a freaking angel. Raphael had switched back and forth between sexes without giving it a second thought. Maybe gender just works differently in heaven. So if Dean were in love with Castiel, angel of the lord, he’d probably get a free pass.
Again. Freaking angel.
And while they fought to stop the apocalypse, when Castiel was still all wings and glory and purpose, that would have been fine. Castiel was the galaxy inside a dweeby PTA Bible-thumper. Jimmy Novak was a man. Castiel was infinite light, and if Dean were to fall in love with infinite light, no one could blame him.
But somewhere along the way, the line between Jimmy Novak’s body and Castiel, angel of the lord, blurred to the point of being indistinguishable. Somewhere along the way it’s not just a confused Dean violently jerking off in the shower to sparks and wings, to the head tilt and the squinted eyes and the grinding voice. Somewhere along the way Dean starts glancing over at the angel in the passenger’s seat and blushing a little in spite of himself at the way the collar of his shirt falls open, showing off a few glorious inches of smooth, pale skin. Somewhere along the way he stops being Castiel, angel of the lord and just becomes Cas. Somewhere along the way, Cas watches Dean as he’s sleeping some nights, then Dean feels a twinge that he doesn’t want to identify on those nights he isn’t there.
It doesn’t escape Dean that even the archangels have to abandon their vessels and get replacements, and that Cas has had everything under the sun happen to Jimmy’s body and yet it still stands. It doesn’t escape him when Metatron robs Castiel of his grace, his angelic essence, that the thing in Jimmy Novak’s body is still absolutely Cas. He has no grace, and he’s an angel so it’s not like he has a soul, so Dean doesn’t know what Cas is anymore, exactly.
But whatever he is, Dean is in love with that.