Is repentance accepted if its reason is marriage to a committed girl, and it is not purely for the sake of Allah the Almighty?

Repentance from all sins is immediately obligatory, whether the sins are minor or major. It is not permissible to delay it. If one delays it, one disobeys by that delay. Repentance has conditions, the most important of which is that it be sincerely for Allah the Almighty, seeking His countenance. It does not matter if a worldly objective is secondary to that. What is forbidden is for worldly gain to be the primary objective. It must be noted that marriage is the best guidance for two people who love each other, and that publicizing a sin is more dangerous than committing it secretly.