It is very possible that sexual behavior, like any other, is a learned behavior. Classical conditioning, reward of heterosexual behavior, punishement for homosexual behavior, modelling, and all other modes of learning may well be involved even in sexual orientation.
If so, with homosexuality becoming increasingly more accepted in society, we might expect its incidence to increase as well.
Many historians understand homosexual behavior to have been a norm between mature men and younger boys in classical Greek and Roman times.
Most, if not all human behavior, may be undrstood as being learned. there is no real reason to believe that sexual behavior need be understood to be any different.
Personally though, I would doubt that classical conditioning would work in a lot of cases. Childhood sexual experiences and dysfunctional and horrendous heterosexual experiences can have more powerful effects on our behavior than anything that any trained professional can ethically repicate in his or her office.