The One Where Harry Really Doesn't Have Ten Cats

"Mate, you can dress him up in a tutu and upload it to YouTube, I don't care as long as he's alive when I come back."

Harry gasps. "How did you know I have three tiny cat tutus?"

"You sound like the crazy type."

Or, the AU where Harry is a pet-sitter for the rich and famous, and Louis is rich and famous.