The pair, who have been on and off since 2010, spent the past few days together, riding on Bieber's three-wheeled motorcycle Can-Am Spyder and celebrating good friend Alfredo Flores' birthday in Los Angeles on June 16.
"Justin and Selena are definitely full-on back together at the moment," one source tells Us. "They spent all day riding together on a Can-Am Spyder on Sunset Blvd. … Justin drove while Selena sat on the back holding on to [him]." The source adds: "He was incredibly sweet with her and they looked super happy and in love."
Later that evening, the couple helped their good friend and music video director Alfredo Flores celebrate his birthday at L.A. hotspot Bootsy Bellows. In an Instagram video posted by rapper Khalil, Gomez and Bieber can be seen partying with Flores in the club's private back room, while a bottle waitress brings Flores sparklers and a cake.
Another source tells Us Jelena "looked like a couple" and were "all over each other" at the fete.
A third source tells Us they're not surprised the couple has reunited—but don't expect them to be together long.
"It is always on-and-off," the source close to Bieber tells Us. "Same story, every other week, every year. Now they are together again, next week they won't be." But, the source adds, "They never stop talking, even when you don't see them together—that never changes. They fight, take a break, and then get back together. No surprise that it happened once again."