With his band, Smashing Pumpkins, calling it quits yesterday after 13 years together and 22 million albums sold, lead singer and guitarist Billy Corgan, 33, is at loose ends. He told the Chicago Tribune: “I haven’t been this unstable in seven, eight years.” He called the split “very stressful,” but “the right thing.” He added that he plans to take off for a year to “create a little bit of space between me and what people think of me . . . I want to be sure if I play music again that I’m really confident about what I’m doing.”