Spoiler: I don't think it's possible for something to be too gay, but as a nonbinary lesbian who almost invariably writes about lesbians and nonbinary people and the Venn diagram connecting them, it's something I worry about when I'm writing. And why should I? Well, aside from the internalized biases that make it impossible for any marginalized person to feel 100% great 100% of the time when writing about characters like them—that's a given.
Instead of explicitly answering this question, I'm going to recount some of my experiences with representation and then weasel around to how I really feel about stuff like this.
First off, the hegemony of cishet white people writing about stuff convinced me I didn't like entire genres of literature. I'd never read science fiction I liked until I read Binti. I hate Wuthering Heights. I love Mexican Gothic. Wheel of Time bored me to tears and Gideon the Ninth laughed me to tears. I spent a solid three years of my life as a non-reader—or more specifically, as someone who didn't read for pleasure because I didn't know where to look.
When I did start reading for pleasure and found books that were really and truly fresh and fun and exciting, it was kind of life-changing for me. And it validated my writing process! Who knew, right? Reading new books gives you a better perspective on reading and writing!
Despite all the great books I've read in the last year and a half (and I had a lot to catch up on!), I'm still starving for stuff that I can see my own experience as a lesbian in—something that messes around with gender and promotes a rightfully trans-inclusive understanding of what lesbian means. There are trans women who are lesbians, there are nonbinary people who are lesbians, and lesbianism is a fantastically nuanced thing. I want that in the things I read and write, and I want to be able to put it out there in the world.
Most importantly, I want they/them and he/him and trans lesbians in speculative settings—in fantasy and horror and scifi and all the genres I've discovered I love. If I'm physically capable of writing them, why shouldn't I go for it? Why shouldn't anyone go for it and make their experience heard without having to contend with fear and shame and regret and worries that people will call it too gay? It's not too gay. It's never too gay.
Can you tell I'm writing this blog post as a form of self-encouragement while drafting my third consecutive manuscript with a main cast entirely comprised of women who like women? Probably not. I'm very subtle.