Your parents were old friends of the Winchesters. Your dad was specifically close with John. Like brothers. So, naturally you grew up with Sam and Dean. While you were close with both of them you were closest with Sam. You both had visions, shared the same birthday and age

You guys had been staying at a motel for a week or so in a small town. It was a pretty boring week. No cases. No nothing. Until tonight

Sam was in the bathroom washing his hands when he started getting a headache. He instinctively started rubbing his eyes before he started getting painful flashes of visions, squeezing his eyes shut as he gripped the sink edge. Of course, whatever bond you guys had meant you were experiencing the same thing out in the room part

You both got flashes of a small town, a guy going into a gun stores and shooting the owner before shooting himself

Dean opened the bathroom door to find Sam gripping the sink tightly, shaking and sweating after the vision had ended

Dean: “Sam. Sammy what the hell”