First- keep writing!

Second- I cringe when I read "both sexes". You damn well know there are more than two genders- does your work speak to that at all? If, your world contains only a strict "both sexes" - what are they? Since they are not exact parallels to human biology (as human biology is more complex than two) your readers may need some help to discern between sex and gender here. So, what is gender in a world with such a strict duality of sex? This seems especially important given that every single one of the beings of this species shares them same sexual orientation.

Second- Your world puts forward an opportunity to explore "the uniqueness of queerness" by having a character realize they are only attracted to folx of one gender (same or not). The "stranger in a strange land" trope could be seen as lazy- but, it could add some texture to the world. It seems unlikely that in any group of beings all of them would share sexual orientation. I'm emphasizing this point because it is likely this total uniformity that your friend is troubled by.

Lastly- putting works of fiction out into the world will open you up to all kinds of criticism. Get ready!