Should the questioner return to his former wife whom he divorced, or should he marry the girl he promised to marry and with whom he committed forbidden acts?

We advise you to return to your divorced wife and to hasten to repent to Allah Almighty for the forbidden acts you committed with the girl you promised to marry. Part of your repentance is to cut off your relationship with her, to abide by the limits of Allah, and to close the door to temptation.