This is a tough question to answer with certainty, since “proving” whether someone’s attractions have changed is sort of like proving whether they were abducted by aliens. It could have happened, but if it did, the only way to know is by taking their word for it. After all, no one can really know how another person feels inside.
If we do take people at their word, what we find is this: Most gay people have tried to become straight at some point in their lives. Many gay Christians have spent years of their lives praying for God to make them straight, and a lot of us have combined prayer with Christian therapy, support groups, psychological treatments, or other methods of seeking change. Some have even undergone controversial therapies like shock treatment, hoping it would help them become straight.
Today, there are a number of “ex-gay organizations,” which teach that gays can become straight. You may have heard the testimony of ex-gays, people who say they’ve changed from gay to straight, usually with God’s help.
The term “ex-gay” can be a bit misleading, however. Often, people who say they “came out of homosexuality” mean only that they stopped engaging in homosexual sex. They consider themselves “ex-gay” because of a change in their behavior, but they continue to be attracted to the same sex. (This is sort of like a prostitute who becomes fed up with her unfulfilling lifestyle and chooses to give up sex. She is still heterosexual, but she is no longer engaging in heterosexual intercourse. She didn’t “come out of heterosexuality.”)
Some ex-gays marry a member of the opposite sex, and use this as the “proof” that they have changed. But many gay people have also married a member of the opposite sex and even raised a family in an attempt to change their inner feelings. Even so, on the inside, they still remain attracted to their own sex. They’re still gay.
The vast majority of ex-gays admit to continuing same-sex attractions, even though they may not say so in their public testimonies. There are a few, however, who claim to have gone from 100% gay to 100% straight. It is possible, then, that an orientation change may be possible for a small percentage of the population. On the other hand, critics will point out that several ex-gays who claimed to have become straight were later caught in compromising situations, demonstrating that they hadn’t always been honest about their innermost feelings.
Ultimately, of course, none of us can say for sure whether it may be possible for some people to change their feelings, or if so, who can change and how much.