Their is plenty of scientific evidence that homosexuality is not genetic to add to the fact that people can change. For example one study (Bailey, J. M. & Pillard, R. C. (1991). A genetic study of male sexual orientation. Archives of General Psychiatry, 48, pp. 1089-1096.) looked at twins.
They found a concordance (both twins homosexual) rate of 52% among identical twins, 22% among non-identical twins and a 9.2 % among non-twins. This study actually provides support for environmental factors. If homosexuality were in the genetic code, all of the identical twins would have been homosexual (1991).
See also here.