While it's difficult to actually 'prove' if HRT is responsible for a 'change' in sexual orientation, It's a common belief held by quite a few people. I do think that it seems to coincide enough to be more than just a coincidence. But for myself, I was confused even before HRT. Before I started testosterone, I was claiming to be a lesbian, but once I started T, I realized that it just didn't feel right, and began to identify as a gay transman. In my case, I believe that I became comfortable enough with who I was to eventually accept my own feelings. But it's hard to say.