Selena Gomez showed major love for Demi Lovato at her "It's Not That Deep Tour ... and TMZ has learned their longtime friendship came full circle. Video shared online shows Selena sitting in a balcony seat with a friend, watching Demi's opening night in Orlando, FL on Monday ... smiling and locked in on the show. Witnesses tell TMZ ... the support started even earlier when Selena and Demi were seen reuniting backstage before the concert, sharing a very sweet, personal moment. We're told it