Well, it depends. If the story is simply exploring the challenges and taboos that gay individuals face in a society that has been historically unaccepting, it might not be discrimination. For example, it could be a way to shed light on the struggles they have had to endure, like being closeted due to family or religious pressure. But if it's full of negative stereotypes and judgment, then it's discriminatory.
Yes, it can be. If the 'taboo gay story' is used to marginalize or stigmatize the gay community, it is a form of discrimination. Literature should be inclusive and respectful of all sexual orientations.