What should I do about my fiancée, who lost her virginity with me, and whose family is forcing her to marry her cousin?

One must immediately repent to Allah Almighty for the forbidden relationship and the adultery that occurred, as Allah Almighty says: "And do not approach unlawful sexual intercourse. Indeed, it is ever an immorality and is evil as a way." One must cut off the relationship with the girl and conceal her [faults].