Is it permissible to speak with one's fiancée about various topics, and does that invalidate the fast, especially sexual topics?

If a man proposes to a woman and has not yet entered into a marriage contract with her, she remains a stranger to him. It is not permissible for him to speak with her except out of necessity, and on the condition that there is no private seclusion (khalwa). The prohibition is further emphasized if the conversation involves matters permissible only between spouses. This type of conversation does not invalidate the fast unless it leads to the emission of madhy (pre-seminal fluid) or maniy (semen).