I want to know if it is a sin if I allowed other guy to touch my penis? At some point I enjoyed it, but later realized it was not good. Do I need to confess my sin? If yes, then what do I need to tell the priest?
There is a difference between accidental touches, such as squeezing by people in the locker room, and purposeful touching. I'm guessing that this wasn't just a touch since you mentioned enjoying it. Therefore, what I am assuming is that he masturbated you for a while. Such touching is an act of homosexuality, even if it didn't bring you to ejaculation. Yes, it was a sin, which should not be repeated. The sin is mostly on his part, but you participated in it by allowing it to happen.
Do I assume that the other guy was older than you? It is hard to determine from your note all that took place, but I'm concerned that this other guy may have sexually abused you by taking advantage of the situation.
Whenever a Christian sins there are two things that are required: First, there has to be a change in attitude toward the sin and a change in behavior. "For the sorrow that is according to the will of God produces a repentance without regret, leading to salvation, but the sorrow of the world produces death. For behold what earnestness this very thing, this godly sorrow, has produced in you: what vindication of yourselves, what indignation, what fear, what longing, what zeal, what avenging of wrong! In everything you demonstrated yourselves to be innocent in the matter" (II Corinthians 7:10-11). You can't continue to see the sin as acceptable and you need to make changes so that the behavior is not repeated. Second, you have to confess your faults to God. "If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9).
What you don't find in the New Testament is a requirement to confess sins to a religious leader. Rather there is an encouragement to talk about your difficulties to a fellow Christian whom you respect and trust. "Therefore, confess your sins to one another, and pray for one another so that you may be healed. The effective prayer of a righteous man can accomplish much" (James 5:16). The confession to another Christian doesn't bring forgiveness -- that has to come from God -- but it is good to know that you have friends praying with you for your forgiveness.