How can one become happy and optimistic after repentance, even though the soul blames him daily for past sins, and he fears the impact of his history on his future marriage?

If your repentance is sincere, then Allah will erase your sins, and you will return as one who has not sinned, for the one who repents from sin is like one who has no sin. Reflect upon Allah's Most Beautiful Names and Attributes, such as Al-Ghafour (the Oft-Forgiving) and Ar-Rahim (the Most Merciful), as this brings tranquility. Strive in obedience to Allah and seek His pleasure, and know that true pleasure is attained through obedience, and perseverance and patience are required to achieve it. Proceed on the path of marriage and do not dwell on your past sins, for they have been removed, all praise be to Allah.