Kaidan straightens his already taunt stature when Shepard goes to Garrus' side. He's immediately outnumbered by two people who trust each other with not only the fate of the galaxy, but with each other's lives. It's threatening, even if they don't mean it. Kaidan is the outsider; Kaidan is not the one either of them would choose to have at their side. He still stands up tall under the pressure, never truly loosing his grace; his firm control of the entire situation. If the two left, there would be nothing for him to do and he knows that and they know that too. It's no reason to flaunt it.

"They're making a camp right now. They need some rest, then we'll move on."