What's going on with Justin and Selena's relationship?

Are Justin and Selena exes who are hanging out together as friends…or as something more? Us Weekly says they are definitely dating again: 

"Justin and Selena are definitely full-on back together at the moment." 

Their source added: 

"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]. He was incredibly sweet with her and they looked super happy and in love."

But a second source says don't expect it to last long: 

"It is always on-and-off. Same story, every other week, every year. Now they are together again, next week they won't be. 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."