Huh I just thought of something.
Letters are something you read, right?
Maybe what Caramel is trying to say here (through Yuki) is that love isn't something we approach mechanically, like reading a letter. The letter filled with feelings was a sort of symbol of Yoru/Yuki's love. And you simply can't help buy enjoy it thoroughly. Furthermore we can't enjoy one-sided love, so we accept it and respect it, but we don't "consume" it, to use a word.
Food for thought (pun completely intended).