Is it considered disbelief for a gay person to say, "I am a man"—knowing that Allah is aware of this—and is he required to disclose his homosexuality for repentance, or is it sufficient for him to conceal it and repent privately, continuing to dissemble for the sake of concealment?

Your statement is not disbelief (kufr). However, if you have committed the abomination of sodomy—God forbid—you must repent immediately. If it is merely an inclination without having committed the act, then you must strive against your soul to rid yourself of it. Beware of God's wrath, seek cover under God's concealment, and do not tell anyone. Strive for recovery by resorting to Allah the Almighty, increasing supplications, keeping company with righteous people, contemplating the punishment for this act. You may also consult a mental health specialist or the counseling section of this website.