Our Lord, the creator and sustainer of all things, deemed in his divine plan and purpose that marriage of man and women would be sacred. He created man and women for each other, for them to become one in the perfect love which he had made them from, and that they be joined also to him in sacred bond. This joining of them, this love, is the love that produces life. Any other sexual relationship is not pure love, as there is no care for bringing life or God. The will to bring life into the world is a perfect love and the intended sacred love that God has handed to us, because from him he gave us life through his love. Let me highlight that again, God, through His love, gave us life. If a gay person believed in God, then they would believe what God has declared, that he made man for women and that they be joined to each other, and to Him.
You are essentially destroying your image of God by laying with the same sex. He created man and women specifically for each other, these two together are made in the image of God. When these two join together in perfect love, along with Christ who is the center holding them together, then they complete the image of God. By their perfect love, they will bring life just as God brought life.
We see this in scripture. How can the Church that Christ established go willingly against what Christ commanded?
You are young, your understanding of these things needs to grow. The secular world is a powerful force, it is ingrained in every part of the day. Through commercials, tv shows, movies, books, schools, etc. It changes what we might think to be acceptable. If most of society agrees with and supports same sex marriage, then you are susceptible to being intertwined in their logic. However, if we hold to the truth of what Christ taught, a truth that leads to the source of life, the source of all goodness, then the secular worlds logic crumbles.
Trust in Him who loves you beyond anything or anyone in the world. All he has asked us to do is to love one another, (which doesn’t include supporting someone’s sin), and to love him. And how did he say we love him? “Keep my commandments”. It isn’t a thing out of fear, or merely just a rule, it is much grander than that. It has all to do with the goodness of it, the righteousness of it. The reality of it. The reality that we are doing the Will of the one who holds all things, the Will that is the source of love and life.