That’s also how I always saw Shanks reaction, but imo it does makes sense? In his eyes Buggy just made a decision they talked about before. He doesn’t want to follow Shanks. That’s his decision and Shanks respects that.

But I wonder what he would think if he knew the real reason why Buggy left him?

Also maybe I’m just crazy but I think we never saw Shanks face in that moment. The focus is solely on Buggy reaction

(context)

yeah, this is a part of why i think shanks takes the separation (relatively) well—he thinks to himself, okay, i was wrong about what buggy wanted, or maybe he changed his mind again. either way, i don’t have to like it, but i do have to respect it. and that’s what he does, he respects buggy’s choice and moves on with his life. maybe on certain anniversaries lets himself wonder what he’s up to, hopes he’s doing well.

& you’re not crazy, we don’t really get to see shanks’ reaction. the only panel in that flashback showing his whole face is the one where he tells buggy he changed his mind about going to laugh tale. we see his face in partially shadowed profile (no eyes visible) when buggy reminds him of his old promise and when he asks buggy to come with him. the other panels either don’t feature him at all, or just show him in silhouette.

now, that might not mean anything—the manga art can get a little cramped sometimes, with all the story oda’s trying to fit into fifteen pages a week—but it’s possible oda is intentionally hiding shanks’ face from us. that could be because shanks is trying to hide what he’s feeling, or it could be because what he’s feeling is unusual or unexpected, and seeing that expression would distract us from the story we’re meant to be focusing on at the moment. (there are plenty of visual stories out there that take an age to reveal a character’s face in a particular moment for such reasons; the elric family photo in fma is probably my favorite example.) i think when 1082 gets animated, we’ll have a better sense of whether this was a matter of not having space on the page to show shanks’ face vs intentionally hiding his face from us.

as to your other question, what if shanks knew that buggy left because he’d changed his mind about laugh tale… oof. i don’t know. i think that depends on why shanks changed his mind. and unfortunately for me as a theorist, that’s one of those lingering mysteries i don’t expect to get an answer any time soon! if his reason is serious, and needs to be kept secret, i think shanks might resign himself to buggy leaving. that’s the cost of having unexplained, unspoken goals. if you can’t offer complete trust, you won’t receive it in return.

but if the reason isn’t that important, or doesn’t need to be a secret, i wonder if shanks might have tried explaining himself? though buggy’s stubborn enough i don’t know that an explanation would have made any difference, once he’d declared that he wouldn’t come with shanks.