It isn't easy trying to get Arctus to understand that this place isn't your home anymore—that you're not just taking a trip away, and that you might never come back to live here again. As soon as she realizes what you're telling her, she starts to mew in desperation, and you can tell that she's pleading with you to stay here.
Looking around the little bedroom, where some of your things are still sitting in their usual place, you can't deny it's a difficult thing to refuse. But you know it's impossible—for now, at least. You don't know what's going to happen to the forest, but you can't make promises to Arctus (or yourself) that you can't keep. So you tell Arctus—gently, but insistently—that you need to go home.
"It's not safe here. Grandma told us it wasn't safe. You believe Grandma, right?"
Arctus looks around hopefully, as if expecting to see your grandma coming through the door—but when she doesn't, she lets out another soft noise, and at last you think she understands.
Before you leave, though, you decide to spend a little longer in your old home—and to find one more thing you can take back with you.