Do not be afraid. Your temptations do not affect God’s love for you. During the high school years, the body develops rapidly, spurred on by profound hormonal changes. Because of this, teens are often at a loss to understand all the feelings they experience. Even if a feeling of attraction persists for some time, this does not mean that it will be permanent. I know of many men who were actively homosexual but left that lifestyle and created successful marriages and families. Just because you have feelings that you are unable to explain, this does not mean that God is unhappy with you or that you are incapable of living a fulfilled heterosexual life.
Let us assume, though, that the attractions and even temptations do not subside. I have friends who have homosexual temptations, but I do not speak of them as “gay” or even as “homosexuals.” To do so would be to define them by a label, as if that were all there were to them and all they will ever be. We should not define ourselves by our struggles or sexual attractions. “Homosexual” is not what you are. For one thing, you are a guy with many talents, struggles, gifts, and other characteristics, but most important of all, you are a son of God, and that is your identity.
One day, during an interview, someone asked Mother Teresa for her views on homosexuality. She announced that she did not like the word homosexual. She stopped the interview and told the reporters that if they had any more questions about homosexuals, they would refer to them from now on as “friends of Jesus.” This is how the Church sees those who carry this cross.
It might help to know that you are not alone in what you are experiencing. If you go to the Courage web site, here, you'll find support for those who struggle with homosexuality and want to glorify God with their lives. Another group, the National Association for Research and Therapy of Homosexuality (NARTH) might also prove helpful. Sometimes a person struggling with homosexuality can benefit from counseling rooted in a Catholic perspective. NARTH can help direct people to such counselors.
I am sure this is all frightening for you and you may feel alone. You are not alone. A large fellowship of men and women is growing closer to God while carrying this same cross and persevering in the virtue of chastity. Because of original sin, all of us experience the effects of the Fall. For example, we all have weakened wills, darkened intellects, and disordered desires. Same-sex attraction is only one manifestation of the universal human condition. Therefore, if we accept the fact that our disordered sexual desires are part of our fallen nature, we also can accept the fact that Christ has promised to redeem them. Do not be afraid or lose hope. Come to God in prayer to be loved by him as you are. He will help you do the rest.