Have you just created a new philosophy: Interactionism?
Interaction defines existence.
I’m not sure what the old philosophy is, other than to say, if something exists only for you, then you’re just crazy or foolish. If it exists for everyone, but for no thing, it’s mass hysteria. But if things in the world that we interact with react to it, then we call it real.
But maybe we’re just imagining that, too.