Is what the fiancée is suffering from—her fiancé's emotional coldness and lack of attention towards her—a punishment from Allah for her previous forbidden relationships, despite her repentance two years ago?

Your yearning for the days of flirtation contradicts the repentance which is a condition for sincere repentance. If the suitor is a man of good character and religion, then hold on to him. Be cautious, as he is still a stranger to you, and it is not permissible for him to flirt with you or speak to you with words of love. This is not an affliction for you to ask whether it is a punishment or not. Even if it were an affliction, not every affliction is due to a sin; it could be a test. Allah Almighty says: "And We test you with evil and with good as a trial; and to Us you will be returned" (Al-Anbiya: 35).