My Bloody Valentine shows us that Sam is starved for blood/vitality/POWER, Cas craves “the strange flesh”/meat/SEX, and Dean, ofc, is all about LOVE.
Blood, especially in Christian terms, is vitality—a stand-in for the forbidden consumption of God’s power.
Beef may be a clean animal, but the episode foregrounds meat as desire: the opening scene with the couple tearing into each other underlines the meat/sex consumption that Cas embodies.
And then there’s Dean and LOVE. He explicitly rejects the Cupid’s (rightly suspicious) account of his parents’ story. More than that, Cupids themselves are framed as random, glib facilitators—even outside Heaven’s “important” matches, they cheapen feelings into machinery. Dean refuses that. He needs to believe in LOVE, and it is LOVE he craves to fill the emptiness.