Will I be sinful if I have relations with a non-Muslim woman after separating from her, and what should I do to avoid sins and help her?

Adultery is a serious crime, but Allah has opened the door to repentance and transforms the bad deeds of those who repent into good deeds. Sincere repentance erases the sin, and the fornicator does not bear the burden of what the woman with whom he committed adultery does after his repentance. Repentance is achieved by abandoning the sin, regretting it, and resolving never to return to it, while also avoiding its precursors. One should hasten to marry a chaste Muslim woman, keep away from the woman with whom he committed adultery, avoid mixing with non-mahram women, lower his gaze, and stay away from bad company. One must conceal his sin and not mention it to anyone.