All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
We point out that expressing the falling into immorality as betrayal towards spouses may suggest that these immoralities are only reprehensible in terms of their being betrayal to the wife or the fiancée, not in terms of them being disobedience to Allah the Almighty and transgressing His limits in the first place, which is not right.
If you repent sincerely from immorality, then true repentance erases what came before it. The one who repents from sin is like one who has committed no sin. Rejoice in the acceptance of repentance, Allah's pardon, and His forgiveness, for true repentance is accepted by Allah. He, the Most High, says (what means), {And it is He who accepts repentance from His servants and pardons the evil deeds and knows what you do.} [Quran 42: 25]
He the Almighty also says (what means), {Say, 'O My servants who have transgressed against themselves [by sinning], do not despair of the mercy of Allah. Indeed, Allah forgives all sins. Indeed, it is He who is the Forgiving, the Merciful'} [Quran 39: 53]
Try your best to convince your parents to initiate marriage in order to protect yourself from sin and keep away from immorality. If they do not agree and ask you to delay the marriage, then you are not obligated to obey them because marriage is obligatory for someone who fears adultery, and you are not sinning by disobeying them in this matter, but you must be kind to them.
Allah knows best.