Is it permissible to repent from adultery and abortion, and is the perpetrator considered a murderer, and what is required of him for his sin to be forgiven?

You must repent to Allah Almighty for committing adultery, which is one of the gravest sins. Many jurists permit abortion before the ensoulment, while some do not permit it at all. Based on this, you must repent to Allah Almighty for what happened. You are not considered a murderer, and there is no expiation for abortion at this stage because it occurred before the formation of the fetus.