(//w/// aw no you’re lovelier! i’ll assume if they woke up in the middle of the night?)
Makoto: When he feels that they’re not there anymore, he groans a little and sits up, glancing around sleepily and trying to get out of bed to find them. When it turns out they just went to the bathroom, he laughs lightly and hugs them tighter than usual when they go back to sleep.
Haruka: If he sees them out of bed, he’d be immensely relieved that they didn’t leave him and offer to make mackerel if they were hungry. It takes a bit longer for him to fall asleep if they come back, but he manages to mumble about how glad he was they were still with him before he drifts off.
Nagisa: Once he registers it, he panics, shooting straight up from his bed and checking every room available to try to find them. When he sees them, he hugs them tightly and tells them that he was scared to not see them there, and keeps hugging them until he falls asleep.
Rei: He fumbles around to find his glasses and clumsily make his way around his house, trying to find his partner and would probably end up bumping into them and sighing in relief before going back to bed.
Rin: It takes him a few seconds, but he jumps right out of his bed and grabs his cell phone, calling their number while pacing around his house. When he finds them he scolds them by hitting them on the head and telling them he was worried, grateful for the darkness covering his blush.
Sousuke: Even if he’s so sleepy he can hardly stand it, he still tries to look around for his partner, resting his head on their shoulder when he finds them and tells them not to scare him like that again because he likes it better when they’re next to him.
Nitori: He panics and is wide-awake all over again, hesitantly calling his partner’s name while he wanders around his house to find them. When he does he scolds them for scaring him, and kisses their head when they’re back in bed together.
Seijuurou: He waits a little bit, not believing that his partner would just get up and leave in the middle of the night. He pretends to be asleep until they come back to bed, and then he surprises them by hugging them until they both drift off.
Momotarou: He’d be scared at first, but too sleepy to do anything and might convince himself that he’s dreaming before falling asleep again. When he wakes up to see his partner there again, he grins sleepily and snuggles them, tangling their legs together.