Should I leave my fiancée and return to my ex-fiancée, whom I discovered is not a virgin due to a previous encounter, knowing that my family disapproves of her and that she was the one who left me previously?

It is obligatory to repent sincerely from the sinful relationship and unlawful cohabitation, while reflecting upon the wisdom of the Shariah in prohibiting relations between men and women outside the framework of marriage, as Allah Almighty says: "nor those who take secret lovers" (Quran 4:25). If the girl was compliant, then she brought this upon herself. Marriage to her is not obligatory according to Shariah, nor is it encouraged unless she has repented and become upright. However, if the fiancée is righteous and religious, then hold onto her and do not break off the engagement except for a valid reason, because breaking an engagement without need is disliked. And note that hymen repair is not permissible except under specific Shariah guidelines.