If I recall correctly, even the Catholic Church doesn’t teach that someone can go from gay to straight. The Catechism teaches that homosexuals are called to chaste lives- not straight lives.
Brain chemistry and genetics play a huge part in attraction, but you have to have faith to live such a chaste life. Our duty, as Christians, isn’t to force people to stop living as homosexuals and adopt the chaste lifestyle. It is to encourage our brothers and sister in Christ to pray, to live the life that God has called them to. For non-Christian homosexuals, it’s our duty as Christians to pray for them and lead them to Christ. You have to have faith before any change that large can happen in your life- speaking from experience, as a bisexual living a straight life(because I can- if I were lesbian, I’d be chaste).
The number of men and women who have deep-seated homosexual tendencies is not negligible. This inclination, which is objectively disordered, constitutes for most of them a trial. They must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God’s will in their lives and, if they are Christians, to unite to the sacrifice of the Lord’s Cross the difficulties they may encounter from their condition.
Homosexual persons are called to chastity. By the virtues of self-mastery that teach them inner freedom, at times by the support of disinterested friendship, by prayer and sacramental grace, they can and should gradually and resolutely approach Christian perfection.
So, I’d say Christian Perfection does NOT mean having heterosexual desires- what about those asexuals who have no sexual desire at all? Certainly, we don’t expect priests to live heterosexual lives- they are sworn to chaste lives. We need to encourage, lovingly, those brethren who struggle with this to adopt chaste practices, and show them that chastity really isn’t that bad. We need to encourage, lovingly, those who don’t share our faith to take a second look, to embrace the love and will of God in their lives.