A long time ago (15 years ago) when I was 20, I went to a party. While there, I made out with a guy who was 17 (I think). We did not have intercourse but did a lot of other things including showering in the nude. I have since changed my life and repented for all that I had done previously. I guess I had forgotten about this event and it surfaced the other day in my mind. What do I do? I have prayed about this for days and am sick with shame and disgust with myself. I have begged God for forgiveness. Looking at the laws on the Internet, I think this is statutory rape. I don't even know who he is. What does God want me to do?
You treat one sin the same as any other sin. When a person becomes aware of sin and their need for salvation, they need to make their life right with God by following His commands to become a child of God. The page titled "Things That Accompany Salvation" contains a list of what God says is needed to be saved from your sins.
A person who is a child of God has the right to approach God's throne to ask for forgiveness of the sins he has committed. There are two things God says is needed to be forgiven. One is that you must acknowledge (or confess your sins) to God. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9). God also expects us to change our ways so that we do not continue in sin. This is called repentance. "For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death. For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter" (II Corinthians 7:10-11).
In other words, you have to be willing to say that what you did was wrong and that you now live a life that is contrary to the sinful life you once lived. The fact that the opportunity to ask this particular man for the forgiveness of the wrong you did against him doesn't matter. You can only be expected to do what you are able to do. A murderer can't ask forgiveness of the one he killed, but he can still repent of his sin and live a new life.
It appears you are having a harder time forgiving yourself than God has in forgiving you. ""But if a wicked man turns from all his sins which he has committed, keeps all My statutes, and does what is lawful and right, he shall surely live; he shall not die. None of the transgressions which he has committed shall be remembered against him; because of the righteousness which he has done, he shall live. Do I have any pleasure at all that the wicked should die?" says the Lord GOD, "and not that he should turn from his ways and live?"" (Ezekiel 18:21-23).