Remember him, Selena? Gomez's ex, The Weeknd, rolled into town Friday night in his Lamborghini Aventador SV -- which as a price tag of $500K by the way -- and fans were left wondering if the singer might be trying to win his lady back.

After a two-week stint in a New York rehab for a "tune-up" on her anxiety and depression issues, Selena Gomez was back in LA Saturday, enjoying a sunny afternoon in the park with friends, appearing happier than ever. So what do most ex-boyfriends do right when you're back in a good place, mentally and emotionally? They swoop in and confuse you and make your life hell, that's what!

Obviously Justin Bieber's been doing the exact same thing -- he invited Selena to watch his hockey game the other night when she returned home, no doubt putting her in a confused romantic state. Now The Weeknd's spending time in LA, perhaps seeing an opportunity with his ex. He's not here searching for his other ex, Bella Hadid. She's off in New York visiting her mom. And anyway, Bella's been busy cyber-flirting with Tyga!

Bella recently posted a video of herself jamming to Tyga's new single "Temperature," with pink hearts floating above her head in the Snap, and with her puckering up air kissing some mysterious person ... maybe Tyga? Tyga responded by reposting and tagging Bella. Fans are freaking out -- in a good way -- but neither has commented since. We say to Bella, stay away! The Weeknd was a good guy; Tyga, not so much ...