Is it considered a sin for a young man and woman to exchange affectionate messages for three years before marriage, knowing that they have not met or spoken directly, that the intermediary between them was the young man's sister, and that the messages were of utmost respect and chastity?

A man is a stranger to the woman he intends to marry. Therefore, it is not permissible for him to be in seclusion with her, nor to exchange love letters, nor to engage in any other means of arousing emotions, nor to look at her except when proposing to her, in which case he may look at what encourages him to marry her. Those who asked the question must repent for what occurred between them.