Please help! St. Alphonsus?

St. Alphonsus Liguori is unique in the sense that the Church has declared all of his moral judgements to be sound and reliable for confessors to reference.

St. Alphonsus also says: "Cardinal Pico de la Mirandola, bishop of Albano, forbade the confessors of his diocese to absolve those lovers who, after being duly admonished, continued to hold long conversations together, partieularly if they should be alone, or if the conversations should be of great length, or clandestine, or by night." St. Alphonsus agrees with this decision, and in doing so makes a moral judgement.

Does this mean that it's a sin for couples to have conversations with each other that are lengthy, alone, or at night? I can hardly imagine any modern couple being able to avoid all three. Wouldn't it be a good thing if a man is close with his girlfriend and has lengthy conversations with her, to determine if he wants to marry her? But since St. Alphonsus says no, are we obligated to follow his teaching?