Billy never really cared about his siblings love lives or partner/s. As long as they treated them right and were cool to him, they were fine

But this one was different. Phoebe's newest boyfriend really threw Billy into a loop. Not because of him, but because of his younger sister he'd brung today

Phoebe: "Billy, this is my boyfriends little sister. Now go hangout, me an her brother will be down here," Phoebe said, nudging Billy to leave