I was looking at that D/Kai/Sian/Steven post again, and I noticed something.
Here's Steven. He's sad. He's worried. He's worried about the Sian he knows and what's happened to her, and he's worried about what this could mean for FAN and their mission. He desperately wants Sian back.
Here's Kai. He's sad and worried, but there's something else. Kai is angry. He let someone he knew and cared about get picked up by the Facility, experimented on, and tortured to insanity. Now he's even more ashamed because in the earpiece conversation he realized just how much D cared about him. Yes, he's angry at the Facility, but he's more angry at himself for letting this happen to her. This is him cursing himself for being such an uncaring idiot. He'll stay with D and make up for what he did to her by making sure she's all right, no matter what it takes.
(Liam and Daniel - Is this what you were actually thinking during these shots? If not, feel free to correct me, but this is what I saw.)