I believe it is sinful to reject the gender that God has assigned to you, and the purpose God has assigned to that gender. Persons with homosexual attraction disorder may not be able to live out God's purpose without therapy and prayer; if they were seriously abused in childhood, they may not ever be a good candidate for marriage, and should remain celebate. But to ask society and the church to rewrite the rules so that they can continue to sin is wrong.
How does a homosexual man reject his gender?
By the same token, it is sinful and disordered to be in a sexual relationship of any kind that is outside the bonds of marriage. The ONLY sin-free and ordered use of sexual activity is between a man and woman who are married.