Selena Gomez and Justin Bieber sealed the deal -- 'cause nothing screams we're back together like a chick happily slipping into her guy's sweaty jersey!
Selena was beaming on the ice as she watched Justin's hockey scrimmage Wednesday night in Los Angeles. While they haven't made any official announcement ... c'mon ... no woman's sitting through a guy's glorified practice, unless she's banging him.
Right afterward, the couple left the rink together -- Justin still sweatin' and Selena sporting a hoodie and the jersey.
They're in full-time inseparable mode now.