If Dean had ended up permanently becoming a vampire Cas would have let him drink his blood. He would offer instantly. Dean wants to refuse but Cas is so serious about it and Dean is so hungry....
Amazingly the traces of Grace in the blood negates Dean's craving for humans and he just carries on mostly like normal. As long as they meet up once a week and Dean sinks his fangs in Cas's wrist. Firmly wrist only. It's not weird it's not sexual (Dean tells himself repeatedly, even when they're clearly having a weirdly sexual experience)
Eventually, inevitably, the bite moves to Cas's arm, his shoulder, his neck, his thigh.....
Anyway
Sam has no idea how Dean is able to push aside his cravings and vampire instincts and he keeps asking him how is he doing this he shouldn't be able to do this?? and Dean says I'm just built different idk what to tell you Sammy
Events carry on as they should, but Dean and Cas have their blood drinking sessions in the background of everything in secret :)
