What should I do about the problem of my fiancée, who lived an uncommitted life before our engagement, and my own problems into which I have fallen?

If the woman described with those characteristics existed before the engagement, then it is not permissible to marry her except after sincere repentance to Allah. If her repentance, regret, and avoidance of non-mahram men become evident to you, then it is permissible for you to marry her.

It is advisable to seek a righteous, chaste woman who will be a source of happiness in this world and the hereafter. She will be the mother of your child, the guardian of your honor and wealth, and through her, affection, mercy, and tranquility will be realized. "And among His signs is this, that He created for you mates from among yourselves, that you may dwell in tranquility with them; and He put love and mercy between you." The Prophet, peace be upon him, said: "A woman is married for four things: for her wealth, for her lineage, for her beauty, and for her religion. So, succeed with the one who is religious, may your hands be dusted." And he said: "This world is a provision, and the best provision of this world is a righteous wife."

As for what emanated from you, praise be to Allah for granting you success in repentance. Repentance must be for Allah, not for the sake of the fiancée. You must renew your repentance, seek forgiveness, and pledge not to return to such actions.

It is advised to lower your gaze, beware of being alone with non-mahram women, keep company with the righteous, avoid listening to music and songs, and be diligent in performing prayers with the Muslims, with their humility and pillars. "Indeed, the believers have succeeded, those who are humble in their prayers."