There's an old saying about friends and enemies, and keeping one close and the other closer. But she doesn't believe in sayings. They're silly things, so-called wisdom that logic disproves easily enough, and she is nothing if not logical.
Keep friends and enemies equidistant. Arm around one, hand tangled in the other's hair. Fair enough. She props herself up on one elbow and peers over Harry's head at a pair of cool gray eyes. There's attraction there, if one knows to look for it. They call each other by their last names and it makes perfect sense to them. It's like a reminder. Enemies, remember? Except you don't kiss an enemy and you don't share a bed with them, and you certainly don't throw a wrench into the whole complicated mechanism by adding a third person.
And that's the reason they're both here, isn't it? She's the order and Malfoy's the chaos, she's safe and he's anything but, and somewhere in the middle is Harry. One of these days someone's going to bring up love triangles. Maybe she'll write an essay on it, all neat and tidy, and reduce the whole mess to a formula. Only it's less geometry and more catastrophe curve. It's telling who's always in the middle, after all.
Maybe she should be scared that she's gotten used to this, or that she knows what Malfoy's going to ask before he opens his mouth. Of course she shakes her head to preempt him. There's a baring of teeth, 'don't you dare wake him up' hiding the more primal 'mine', and part of her marvels that she can have a battle of wills naked in a bed with her worst enemy and her best friend.
Malfoy catches her wrist as she reaches protectively across Harry. His free hand is resting on Harry's chest and her fingers are caught in his black hair, and maybe one of them should stop to ask who's the real anchor here. Instead they just glare. They always do this. Sometimes it ends with a hex and sometimes it turns into a kiss, scholarly proof of the thin line between love and hate.
This time Harry stirs and opens one eye, peering at them. They end their staredown and look back at him. She knows he feels like he should choose, but she can't allow that and Malfoy can't either. A middle requires two ends. A triangle needs three sides. Order and chaos and geometry, and she wonders if all emotions can be reduced to proofs and conclusions. Maybe someday she'll tell Harry about equidistance.
But not Malfoy. She feels his grip on her wrist tighten, holding the triangle together, and figures he already knows.