Is it permissible to divorce one's wife if love for her has vanished from the heart, in addition to discovering past conversations she had with a young man before marriage that she denies?

Lack of love alone is not a reason for divorce, as there may be other interests that outweigh the interest of love. If the wife repents of her past actions, do not dwell on the past, and live with her kindly. If you see that separation is better for achieving interests, then release her with kindness, for Allah may replace for each of you something better than what was left, and "divorce may be one of the greatest blessings."