How can the perpetrator be clearly unjust to the girl, when she is obligated [by religious law] and participated in the sin willingly? Can this act be a reason for him not entering Paradise? What must he do towards her so that God may be pleased with him? And do sins not entail legal consequences, and transgressions have no sanctity?

The questioner has wronged himself by establishing a forbidden relationship with a girl, and she too has sinned. However, since he has repented with sincere repentance, Allah will accept his repentance, and "the one who repents from a sin is like one who has no sin." A forbidden relationship does not prevent entry into Paradise, for Al-Bukhari narrated that whoever says "Lā ilāha illallāh (There is no god but Allah)" and dies upon that, will enter Paradise, even if he committed adultery or theft. It is obligatory upon the questioner to cut off his relationship with the girl unless he has fallen in love with her and can marry her, along with a commitment to repentance, for the Prophet, peace and blessings be upon him, said: "Nothing like marriage is seen for two who love each other," meaning that the best cure for infatuation is marriage.