Jason's return to Pretty Little Liars brought more to the show than just an attention-getting new hairstyle and a whole lot of jokes about it. He's back in town to prevent Alison from getting taken advantage of by Mary Drake (took you long enough, Jason), but that doesn't seem to be all he's here for. Jason gave Aria a call that led to a pretty interesting conversation – and some intense staring. So what happened between Aria and Jason on Pretty Little Liars?
Luckily they don't keep their conversation veiled for too long. Aria picks up on the fact that Jason is vibing her pretty hard – and honestly, with the force of that staring it would be impossible not to notice – and makes sure he knows she's engaged to Ezra before inquiring whether or not he's told anyone about them. Jason and Aria had a flirtation years ago but it never came to much, in part because she always had Ezra goggles; apparently in the five year time jump Jason and Aria found their way to each other again. They've also kept it a secret all this time, so it obviously wasn't longterm enough that they needed to mention it to anyone. However, there might be more to it than there seems considering how into her Jason clearly still is.
One interesting thing is that Jason asked if Aria was engaged to Liam, her cute newspaper boyfriend, so he obviously knew what Aria was up to after whatever happened between them. It's possible he heard about it from Alison, but what if there was a little...overlap in Aria's relationships? She could have been involved with Jason and Liam around the same time, which might be one reason she wanted to keep her fling with Jason quiet. Aria did cheat on Liam with Ezra, so it's not like that's out of the realm of possibility for her.
Despite the fact that their relationship seemed casual, Jason is definitely holding a little bit of a torch. Aria was the first person he called for help to convince Alison that Mary is shady, as opposed to someone like Spencer, who is at least family (and is the most capable of the girls, let's be real). Aria's wedding is looming and it wouldn't be TV without some obstacles keeping her from going down the aisle. A surprise resurgence of a little romance with Jason might be just the thing to upset her plans for the moment.
One thing is for sure – whatever it was they had in the past doesn't seem to be entirely gone.