AFFAIRS AREN’T meant to last, so it was inevitable that Andy Butler would have to retool after his group’s dance-quake debut. With former guest vocalists Antony Hegarty and Nomi Ruiz pursuing their own careers, Butler is still probing the garage disco sound he nailed in 2008, but with much more restraint. That said, deep house rules on Blue Songs, from the throbalicious “Step Up,” with Bloc Party’s Kele Okereke, to the Arthur Russell-ish “Answers Come in Dreams,” with Aerea Negrot.