Is it obligatory for the questioner to definitively end the relationship with a girl with whom he previously committed Sharia transgressions, especially after she was afflicted with a chronic illness, and there is fear of that affecting her health? And what should he do to atone for what he has done?

Islam came for the happiness of humanity and to prevent evil. Therefore, it prohibited relations between the sexes outside of a valid marriage to block the means [to sin]. What occurred between you, including kisses and seeing her semi-naked, is a seduction from Satan. You both must repent to Allah and completely sever the relationship with the girl, for speaking with her is a gateway to temptation. There is nothing comparable to safety. Do not pay attention to the satanic thoughts that justify the relationship to you. If the girl repents, becomes upright, and you wish to marry her, that is good, for marriage is the best cure for ardent love. The Messenger of Allah (peace and blessings be upon him) said: "There is nothing like marriage for two who love one another." If marriage is not feasible, then each of you should go your separate ways.