Walter's double-life is catching up with him.
Under the power of anesthesia, Walter mentions something to Skyler about his multiple cell phones. When she confronts him about what's going on, he admits everything (well, mostly everything). Tired of his lies, she takes the kids to give Walter time to pack up his things and move out. But he's not about to go down without a fight. And even takes his anger out on one really, really big pizza.