S1·E67 After You've Gone

Lum's Stormtroopers throw Lum a party, but Ataru spoils it by yelling at Lum and accusing her of ruining his life. Lum leaves for her home planet, and when she doesn't return, Ataru, believing she has gone for good, begins to miss her and tearfully wishes she would return. However, it turns out Lum merely left to renew her passport.