Okay, so I don't want anyone to start warring or anything, but I can't help but notice that there might be some form of attraction on Demetri's end when it comes to Alice. You don't have to agree and please don't hate, but I'm going to observe this... And please, this is only specific for the films...
So they came face-to-face for the first time on-screen. The very first moment that Alice enters the castle, Demetri sort of bends around Bella and Edward to see her, even though there would be no need to. He even smirked slightly adoringly when she said, "You wouldn't wanna make a scene." There's an almost flirtatious tone to his voice as he says, "We wouldn't." Later, in the lift, he risks a brief glance towards her.
Alice probably should have seen Demetri going for her, so how is he able to grab her? Its probably just me, but he looks awfully comfortable holding her. When Alice cries out for Aro not to kill Bella, Demetri's staring at her intently, apparently not believing that Bella will be turned into a vampire. As soon as she explains her vision, however, it seems to dawn on him. He seems sceptical when Aro beckons Alice closer and almost reluctantly lets her go, keeping his hand extended briefly afterwards.
Breaking Dawn - Part 2
When Alice returns for the confrontation he steps forward to stop her. He restrains her. Alice reaches over him to offer her hand to Aro and he lets her pass. Demetri then slaps Jasper. *hint hint*
In Alice's vision, Demetri kills Jasper and seems very happy about it. Coincidence that Jasper so happens to be Alice's husband?
So I may be over-thinking this, hell, I probably am. And don't get me wrong, I love Jalice. But the possibility of something else here really grabbed my attention.