Dean knows that Castiel loves him. Loves him wholly, completely, in a way that is totally inhuman but all the more precious for it. Dean knows this. After all, Cas has risked a fall for Dean, been injured protecting him, taken on an archangel for him. Started feeling because of him. Even now, when it is all over, Castiel is still there.

In the beginning Dean was afraid that this would tempt him. Because how can he not be in love with his angel? The angel who taught him trust, and faith. Who understood him from the very first and is always there when Dean needs him. He loves Castiel's nobility, his devotion, his innocent wonder at simple things. And, because Dean is not a strong man, not really, he was – is – terrified of the temptation to tempt Cas. He knows, if he ever lets himself go, that he can drag Castiel down too far before his angel realizes what is happening. He could make an angel fall.

But he has never been tempted. Oh, he's stolen an extra touch here and there, but he's never had the urge to seduce his guardian. The knowledge that such thoughts and lusts would never even enter Cas's head keeps him safe. For an angel, love is about souls. What they share, Dean thinks in his sappiest moments, is too pure for temptation.

Castiel is never hurt when Dean slakes his earthly lusts elsewhere, merely politely uncomprehending. He probably thinks of it as just another human thing.

Dean looks forward to the day he will see Castiel in all his heavenly glory, when the body binding him gives way to perfect celestial harmony for them both. Till then he loves and lusts separately, and keeps his angel safe from himself.