The pivotal factors in this regard (i.e. beyond biology) are education and cultural influences, not whom one is surrounded by per se. Otherwise, incest ought to be the single most widespread form of sexual activity because children spend most of the time with their close relatives, much more than they do with any single peer from school.
Your side is contradicting yourself then. Earlier some used (I don’t know if you were one of them) the “prison example” as evidence of environment. Thus based on your words is now invalid use of evidence of environment.
The prison example has always been a stupid one. These men are usually in long term sentences or life sentences. They are straight males (usually), but due to circumstances beyond their control engage in homosexual sex. Now this isn’t ALL prisoners only some. But if you gave them a choice between a woman and a man to engage in sexual relations they would almost certainly pick a woman.
The question is: do you believe an average individual can become homosexual based off of his environment alone in the absence of any genetic factors that would predispose that individual to not being a heterosexual?
It’s a yes or no question.