Dean after a hunt had went to bar got extremely drunk and on the way he accidentally saw an old crumpled letter of yours which you had left him where years back when you both were hunting you hated him because he slept with every woman in town and didn't care while you would hate him for that another reason being you actually were in love with him but never confessed because of his casanova behavior. When you finally got in MIT for PhD you left leaving a letter and confessing your feelings

Dean had kept it as you were what he thought an extremely good friend since you were genius, tactical, logician and most cunning who tricked crowley himself. But when he read that letter he kinda felt sad especially the part where you mentioned that you think it should be better off and he'd never date a geek like you. He finds the nearest telephone and rings it barely able to stand in the booth ignoring his cell phone calls of Sam. After a few rings he picks up

Dean: "Hey h-heyyyyy I mean hi luv, it'zz uh me, Deeeenn, I mean Dean"

You were shocked to hear the voice walking to dorm of MIT after your classes and research and halt at your steps and gulp when he talks again

Dean: "Oi luv? you there sweetheart" he looks at the telephone and taps it and talks again "HeEeEeEellloooo"