How can one atone for the sin and guilt of breaking off an engagement, especially after some minor transgressions occurred during the engagement period?

Dissolving an engagement is permissible for both parties, but it is makrooh (disliked) if it is without a valid reason, and mubah (permissible) and not makrooh if there is a valid reason for the dissolution. Repentance is obligatory for any transgressions that occurred between the engaged man and woman, by abandoning the sin, regretting it, and resolving not to return to it, while concealing one's own faults and those of the girl, and not publicizing the sin.