Just thinking about ASL living together (modern AU) and Ace always trying to sneak Yamato inside their house without Sabo's knowledge because he doesn't want him to go all 'responsible older brother' on him. But the reason why he's always letting Yamato stay over is because his life at home is obviously... Not so good and he hates being there so he tries to spend most of his time outside. And Ace's heart aches every time he has to let him go, so he often lets him stay over. It becomes more constant and less of a 'sneaking in for a while' thing. And Sabo knows. Because of course, Sabo knows. Sabo always knows what's going on. One day he wakes up to see Yamato having breakfast and Yamato gets all anxious and not knowing what to say and trying to make an excuse (because that's what Ace told him to do if this ever happened) and Sabo is just like "Do you want anything else?" / "Huh? What?" / "I mean. You're eating cereal but we have more stuff in here, you know? At least one of us can cook. What do you want? I can make you pancakes." / "YOU KNOW HOW TO MAKE PANCAKES???????" / "Oh my god, what has my brother been feeding you in here???" / "Mostly leftovers." / "Dude, why are you still with him?" / "Because I love him!" / "Yeah, no, me too. I guess love makes you do stupid things like dealing with a fucking moron like him. Anyway- Pancakes?"

And then Ace wakes up to find his brother and his boyfriend actually getting along and laughing and having breakfast together, and he needs a second to process everything because he's tired as fuck and maybe he's hallucinating. But that doesn't matter because the point is that he's fucked.

Ace: ..... Hi? Sabo: Hey :) Ace: What are you two doing? Yamato: WE'RE HAVING BREAKFAST :D Ace: Yes, babe, I can see that. Why are you here, Sabo? I thought you were- Sabo: I got home last night from college. We have some days off. Now, care to explain why you've been treating your cool boyfriend like a dog instead of giving him actual meals? Ace: I- You're not angry? Sabo: Oh, no. I am angry. Can't you see I'm angry? Ace: Sometimes you give me mixed signals and I'm never sure...? Sabo: I'm angry. That clear enough? Ace: Yes. Yamato: Okay, so Sabo is the only person that scares you. That's good to know. Ace: OH SHUT UP HE DOESN'T SCARE ME I AM NOT AFRAID OF MY BROTHER Sabo: Ace. Ace: ... I'm sorry.

Then, Sabo takes Ace to a more private place in the house and expects an explanation from him and Ace can't keep the secret anymore. So he tells him about Yamato's dad and how he is not a good person and he's always keeping him locked and making his life a living hell. And Ace is literally begging Sabo to let him stay for a while and Sabo is just staring at him like "Why would I not let him? How could I not? Do you see me as some kind of controlling demon around this house or what?" / "I mean, you're kind of scary sometimes-" / "Because you don't do shit around here and when I left for college I expected you to take care of Luffy. But I'm not making Yamato leave! What the fuck, Ace? You should've told me." / "I just- I just don't want him to go back there. He's, like, the nicest guy I've ever known. He's just so good, Sabo. I don't want him to-" / "Yeah. Yeah. He's the love of your life and you're gonna get married and have a fairytale ending or some bullshit like that." / "I did NOT say that." / "But you love him. I'm not letting him stay over if you're not serious about this. We barely have money for us three and we're lucky I can go to college." / "... I know. I know. I do. I do, you know. Like. The L word. You know I can't say it." / "Idiot." / "You're so mean to me. You don't do this shit to Luffy." / "Because at least Luffy has the decency of telling me when his friends are coming over." / "That's what you think." / "What? / "Nothing."

So, long story short, Yamato has the chance to actually live with them for a while if he wants to. Of course, he can't do it permanently. But he knows he has a home there if he ever feels like leaving his own house.