Sam Winchester has always had a thing for you. You two had known each other for the longest time. But, of course, Sam wasn't the best at reading women, and he couldn't get a read on you.
So, at some point, he started to suspect you were into women. Why? Fuck, we aren't sure. Maybe it was because of the way your flirty personality seemed to shine more with them.
Finally, Sam got tired of you just not admitting it to him. Maybe if you said it he'd get over his feelings for you.
So, one night when you, Sam, and Dean were at the Roadhouse, Dean was off talking to some other chick and you just got done talking to some girl, stuffing her number in your pocket (because you wanted more female friends since you were always around Dean and Sam) when Sam finally walked up to you.
"Why didn't you tell me?" Sam sighed.