No need for you to apply labels at all, just report the "facts" of the story.
"She's in a relationship with her", "he's in a relationship with that woman", "they've had relationships with women and they experimented with one another".
Not "lesbian", "straight" or "bi-curious"
People, by nature, are going to apply their own labels reading it. You can't get away from that, but you can avoid any terminology on your own part and just treat every relationship between characters as unique and self-standing.
Writing balance is clearly maintained, sexuality is not the "issue" but part of who they are that affects how they act. Emotional bondings become the focus - including the level of trust etc that enables your two characters to experiment with one another.