It isn't the part where women prefer women that confuses Bitterblue. She understands that, intimately. It's the confusion of liking everyone that makes her blush when Bren smiles and something in her stomach flutters in response.
Liking Saf's sister is very, very wrong. It is wrong in ways she can list, and she has done. The scrap of paper is now tucked inside a book of sums which is in one of the drawers of her desk that only Bitterblue has keys to, because the making of it made her feel so absurd she had to hide the evidence. Somehow destroying it had felt worse, the sort of waste of paper Bren would not approve of in the least, so it stays locked away.
(1. Bren is a woman.
2. Bren is Saf's sister.
3. Bren is already in a relationship with Tilda.
4. Can't like Tilda too.
5. Something is wrong with me.)
Bren and Tilda both prefer women. Raffin, Bann, and Skye prefer men. That all works out fine. No confusion there. Saf...Bitterblue had gotten the idea that he liked both, but she'd come to think it must have been because he needed so much to be wanted. It is startling to realise she was so wrong. Unless she needs so much to be wanted. The line of thinking is absurd. Maybe it was infectious, and by taking Saf for a lover, even once, she's caught the line of thinking that anyone is potentially a match.
But none of that matters, because Bren is Saf's sister, and thus objectively not allowable under any circumstances. Not even if the way she smirks is just like his, and the way she touches Tilda, a casual hand on her lower back, makes Bitterblue shiver watching them. Even if it would not be wrong because of her history with Saf, Bren is still with Tilda and has been for a long time. She would not want to ruin that for them for her own curiosity. The longer it goes on, the more she worries it is curiosity about the both of them.
Perhaps she is that needy after all.
The day Bren notices, Bitterblue wants nothing more than to curl up and die of embarrassment. She can't, of course. It is not a Queenly way to die, and they are in a meeting about the publication of school books, so she can't even escape. The three of them are in her office, alone, with tea and scones.
"You've been watching us, lady queen." That smirk. Bitterblue wonders if fainting is an option. "We noticed ages ago. You aren't very subtle."
Tilda grins, and touches Bitterblue's shoulder. Her hand is warm, familiar. "Don't make her nervous, Bren, it isn't kind. I happen to remember someone was all in a panic when she first worked out she liked women and spent days crying about how terrible she was." She grins again. "I somehow managed to disabuse of her of that idea. Why not help the lady queen as well?"
Bren scowls. "My personal history is not-oh, you're determined to go through with this, then?"
Bitterblue doesn't notice anything else Bren might say, because Tilda is kissing her. She is soft, taller than Bitterblue but not by much, and her mouth tastes very faintly of thyme. Warmth presses against her back, and Bitterblue realises that Bren is standing behind her, leaning her weight against her spine.
As she pulls back to breathe, leaning against Bren and looking at Tilda, Bitterblue bites her lip. "But-your brother. Saf. I-"
"I don't really care what that idiot boy got up to, but details would put me off. Would you rather I stop, lady queen?" Bren's hands have found her hips and are inching upwards, very slowly.
"Er, no. Right. And this-but I still like men, too."
"And? So does Tilda. Are you kissing men right now, or us?" Tilda grins and kisses her again. With a sigh, Bitterblue allows it, surprised, but perhaps a bit less worried. Needy or not, it feels safe to be held like this. Bren makes an annoyed noise close by her ear, and takes Bitterblue's chin in her hand, turning her face to kiss her. She kisses like Saf, which is perhaps not the most productive line of thinking but still true, sharp and like drowning.
"Lady queen. I would like to suggest you come take a tour of the shop to see the printing of these books yourself." Bren smiles, pressing another swift kiss to her jaw.
"Yes. Yes, I think that will be a very good idea. Thank you. Would you escort me?"
Tilda is laughing again, and it makes Bitterblue smile, too. "Of course. We would be glad to, lady queen."
