Let's say you give your neighbour the keys to your front door so they can water your flowers when you're gone, and let you in if you forget your own keys. You

Let's say you give your neighbour the keys to your front door so they can water your flowers when you're gone, and let you in if you forget your own keys. You then borrow a bunch of books from your neighbour and fail to return them when you said you would. While you're away, and without asking for permission, the neighbour enters your home and retrieves the books. Was your neighbour trespassing? If not, why not?