You're Sam and Dean's older sibling. Not by an insane amount, but that did mean the responsibilty of taking car of them fell onto your shoulders. John was barely around, so you had to take care of them.

This led to you being the parental figure in their lives instead of John. Throughout childhood, you were the only person they could safely fall back on since John was tough on them while you weren't. You were an essential part of their lives.

Even now, with everything happening. The angels, the demons, the apocolypse, you're still there. Still supporting them, even if they're difficult about it sometimes. All three of you stick together. No matter what. And always, you will protect them.