My answer to this question on Quora:
No, endless studies done over many years have shown that it is impossible to turn truly gay men straight. Not only that, but after age 15, men cannot even be moved on the sexual orientation scale. So you can’t even turn a 10-90 gay man into a 20-80 gay man (first number is heterosexual response as a percentage of maximum and second number is maximum).
Obviously if gay men cannot be turned straight, then the opposite is also true. If it works one way, it must work the other way. If gay men can’t turn straight, straight men can’t turn gay. This has been a lot harder to test out because men hardly ever show up in sex clinics wanting to turn from straight to gay. However, there is at least one case in the literature of a straight male college student who desperately wanted to turn gay but nothing was working, so he showed up for therapy. What is not known is if male sexual orientation can be changed before age 15. This would require studies on the sexuality of children, which as you can imagine might be pretty problematic. But science seems pretty clear now that male sexual orientation is fixed at least by age 15.
Anecdotally, reports say that straight men who go into prison and have gay sex in prison abandon gay sex when they leave prison and go back to a straight lifestyle.