I definitely agree that we should avoid biological essentialism, and that both sexual orientation and gender identity can be fluid. However, just because someone was once in a same-sex relationship and is now in an opposite-sex relationship doesn’t mean that they changed from gay to straight, and vice-versa. This assumption can lead to erasure of bisexuals and pansexuals. According to Wikipedia, Cynthia Nixon currently identifies as bisexual, and Chirlane McCray says she hates labels.