What is the ruling on seeking a divorce due to not loving the husband, despite his good treatment, given the existence of a past love that one cannot forget?

There is no need for worry. Suicide is forbidden and leads its perpetrator to greater misery. If a woman dislikes her husband and fears falling short in her duties towards him, she has the right to seek khul' (divorce initiated by the wife), and she would not be wronging him. Nevertheless, immediate separation is not advised; rather, one should pause and exercise reason, as emotions may change after marriage, and there is no guarantee of happiness with another person. You might regret the separation. You should seek Allah's help, supplicate, and strive to forget the other person, as emotional love can be attained with the current husband. If cohabitation becomes impossible, then seek khul'. It is recommended for your husband to agree; otherwise, refer the matter to the Sharia (definition) court. Allah will enrich each of them from His bounty.