[Billy]

This was due to happen. Someone shows him the slightest bit of attention, and he tries it on with him, then as soon as he's rejected, he turns on them? Sound familiar? It should do.
Same thing happened with Rebecca. He liked her, she doesn't like him, so he goes on his mission to turn the house against her. Remember, he twisted the whole thing in the bedroom when Kat was crying, and now he is doing the same with Sara!