Well speaking purely biologically, living life's purpose is to reproduce. In essence a gay person falls outside this, and resorts to human-made institutions of adoption to "reproduce".
Its most likely a brain thing, where they have the sex drive of the opposite sex, like a gay man having the sex drive of a straight woman.
In the end, nothing wrong with being gay, and its most likely non curable with our current technology if your brain has the "opposite" sex drive.
Older and wiser. Still bias and proud though ;)