There is no behavioral trait which is fully determined by nature or by nurture. That's a fact and it's proven by numerous psychological studies. There are many possible theories to nurture increasing the likelihood of a homosexual orientation but none has yet been proven to be fully true.
However, I believe that bad relations with father might be a factor when it comes to male homosexuality. The real question here is: how heritable homosexuality could possibly be, and therefore how much can we modify it?
My personal opinion is that everyone is born with some likelihood of being attracted to the same sex. Some people have it at 0.06 (while 0.92 for not being attracted to the same sex) while others at 0.3 et cetera et cetera. However, certain situations in life, not necessarily bad experiences lead us to lean towards same-sex attraction, for men it could be a too intense relation with women. I have seen a few videos of, for example goats acting similarly to dogs as they were raised together. That could explain feminine behavior amongst gays.
And I wouldn't be so sure that sexual orientation cannot be changed.
Well it IS an interesting topic. To this day, we still don't know exactly what determines one's sexual orientation, and I personally believe that parenting plays a role, is that terrible to say?
