Belo keeps them together. He's the one who stands out the most on his own. Children are supposed to have mothers and fathers. That's the way the world is.
So when Bem and Bela reach that point when they can't be together any longer, where just being in the same city or prefecture is a constant irritation, one or the other of them storms off after a fight. There are unspoken rules. The one who leaves makes sure they're seen leaving, because how terrible would it be if they just disappeared, maybe suffering, maybe captured? The one who's left behind takes care of Belo.
Belo kind of likes having Bem or Bela to himself. When it's just him and Bela, other single mothers have a way of finding them, like there's a secret network. They offer babysitting and hand-me-down clothes, and give Bela all the inside information on who to talk to at the city hall and which landlords are good. Most of the times Belo's stayed in a real apartment, with tatami and an indoors toilet and all, those have been when he and Bela are together. Belo plays with the children of Bela's new friends, and Bela learns about makeup and manicures. It's almost like being normal people.
When Bela goes off, Bem usually keeps quiet for a while before giving Belo a wry look and saying, "Well, why don't we have an adventure?" This means they have to go to the library and look at all the travel guides until they find some place that looks exciting, like secret hot springs, or castle ruins, or beaches littered with giant boulders. Bem doesn't usually let them travel by train, because if Belo got scared or Bem got angry they'd be trapped with no way out. Once Bem got them a ride with a man who was delivering a car from Ichinoseki all the way down to Kagoshima, and the guy taught Bem how to drive so they could take turns. That was fun, even though when they thought Belo was asleep they stopped the car and did the adult stuff Belo hated. Bem took Belo around to see all the volcanoes in Kyushu, and they went swimming in the ocean, and they saw monkeys. Belo likes having adventures with Bem.
Belo doesn't know how Bem and Bela decide when it's been enough time to not be angry at each other any more. He always worries, just a little, like when he goes to bed, that maybe if Bem lost his stick he won't be able to find his way back to Bela. But that's never happened. One morning Bem will just turn up wherever Belo and Bela are, and Bela will let her new friends tell him off for running out on his wife and kid. Or Bem and Belo will track Bela down, and she'll open the door, look at them critically from head to toe, and then sigh, "Well, I guess you might as well come in."
Sometimes Belo gets sick of the both of them, and because he's not a child, not really, not entirely, he goes off on his own. He has to be careful. Bad things can happen to small people. But Bem can be so selfish and Bela can be so mean, and Belo just wants things to be different, sometimes. He wishes he had a real mother and father, ones who take pictures with a camera and work in offices and make hot rice with pickles for breakfast. He wants to have a randoseru and go to school and play dodgeball. He wants to grow up and show Bem and Bela that he can be smarter than they are.
He doesn't know what Bem and Bela do when he's not there. If he's really angry he imagines them smiling because he's gone and going to the cinema and eating ice creams without him. Bem sometimes buys Belo ice cream cones when they're adventuring; Bem doesn't hate money the way Bela does, but he says it's a pain in the ass getting it. Belo likes saying that, pain in the ass, mendokuse-, and he likes that Bela yells at Bem for giving him a dirty mouth, even though Bem probably learned it from her. Bem and Bela are funny, like the men he'd seen once on someone's television who told stories and hit each other on the head. He'd almost peed himself laughing.
Belo can never stay angry long. He thinks it's because he's little, and he has a small head, so there's only so much he can fit in it at once. Bem's been trying to teach him the times tables for years, but Belo gets the numbers all tangled up after three times four. But Belo's happy because he forgets why he shouldn't be, and Bem's almost always sad about something, so Belo thinks being a kid's better. Plus, he doesn't ever want to get rid of his toys. They're better than sticks or whips.
When Belo goes home again, which is usually pretty easy, because he never goes that far, at first glance Bem and Bela look like strangers. Like very strange strangers, not like all the people in the shopping streets or getting off the buses. And then Belo blinks and feels warm right inside because no matter how nice other peoples' families look, this is the one that's his.
Bem will look up at him and smile and say, "Welcome home." Bela will never say that she worried, but she'll yell at him and pretend she doesn't care one way or another whether he ever comes back. But over dinner, or maybe while our looking for food the next day, either Bem or Bela will accidentally mention something that they'd only know if they'd followed Belo, keeping an eye on him even when he was sick of them being selfish and mean.
Belo never says thank you, but he always grins ear to ear. The way Bem and Bela make him feel is how he imagines being human feels.