If there is one person who has actually changed his or her orientation, then there is at least an element of choice. I think it may be genetic as in a predisposition, but as with alcoholics and others, there may well be those who have the predisposition and for some reason never “activate” it.
there has been no "Homo gene." Twin studies, where twins are separated at birth, one is gay the other straight show the same rates of homosexuality, ie. there is not one study that shows a higher percentage of the separated twins being both gay...