What is the sin of this relationship and what are its consequences after the girl's abortion, and is the perpetrator sinful for both adultery and abortion, and is he a murderer, and is expiation obligatory upon him, and is there any repentance for him?

You have committed grave sins through adultery. However, if you did not assist in the abortion and did not approve of it, then there is no expiation (kaffara) or blood money (diyah) upon you. As for the extent of the connection between your sin and the sin of murder, it cannot be answered due to the absence of a specific legal text defining it. The door of repentance is open to you. Allah Almighty says: "And indeed, I am the All-Forgiving to whoever repents, believes, and does righteousness, and then is guided." Allah may transform evil deeds into good deeds through sincere repentance. Hasten to repent by abstaining from sins, feeling remorse, and resolving not to return to them.