Selena’s gotta work out to relieve some stress! Rumors abound that she and Justin Bieber are taking a step back after quickly reigniting their relationship following Justin’s religious re-awakening and Selena’s kidney transplant. That’s a lot, y’all …

We spotted Selena emerging from her Pilates class this weekend, in a sexy Puma sports bra that showed off her impressive abs. And now we’re hearing she and Justin, with whom she hasn’t been seen for a few days, have decided to keep their relationship “low key.” A source tells People magazine, “They just backed off a little from being out there and are being a bit more low-key,” adding that Bieber, 23, and Gomez, 25, are still not officially boyfriend/girlfriend yet “but it’s getting close.” Okay, so that’s good!

So what’s maybe NOT so good, is that Selena’s ex, The Weeknd, was spotted “holding hands” with Beiber’s ex Yovanna Ventura the other night! WTF?! Seems the calm Canadian may be trying to get back at Gomez and Bieber by pulling the ol’ “you date my girl, I’ll date yours” thing. The two were reportedly spotted at French Montana’s birthday party Thursday night, according to Us Weekly: “The Weeknd was there hand in hand with Yovanna Ventura all night. They arrived together. They were holding hands. He was there for a solid two hours with her and everywhere they went they held hands.”

Daaang! Is The Weeknd trying to start something? I HOPE we’re there when they run into each other in a club or wherever — that promises to be EPIC!