Beth, that's who

There's a knock on Jacks door, his heart starts pounding in his chest as he sits up in his bed,"Uh come in." he says nervously

"Hey Jack," says Beth as she walks into Jacks room wearing sleeping shorts and a tank top. "Listen...about the bathroom situation."

"I was just um...check-checking in they were..um," he said fumbling nervously over his words.

Beth stared at Jack in disbelief. "Jack I know you were masturbating with them, you don't have to lie to me."

"I just didn't know if you'd be grossed out or not, being my sister and all." he said looking down at her feet.

"Jack you're my brother, you don't gross me out. And you don't have to sneak around trying to use my panties, if you ever want a pair, just...um, ask."

"Really?" Jack said in shock

"Mhmm, in fact, here's one to get you started, " she said with a smirk as she threw the blue boy shorts from the bathroom at Jack's chest. "Have fun!" She said as she closed the door behind her.

Jack stood up and locked his door. He got nice and comfy on his bed and stroked his cock with the panties until he came inside them.