There was something about Alison waving a knife around carelessly that turned Sarah on.
The way Alison treated her when they first met carved into Sarah like a razor blade. Maybe it was how Alison called her ugly when they looked exactly the same, or maybe it was her high ponytail and yoga pants. Whatever it was that ignited this feeling, Sarah doesn't remember. (And she doesn't think she wants to, either.)
It got worse when Alison was teaching her how to shoot. Sarah couldn't help but feel jealous when Alison mentioned Beth like they were lovers. She knew how ridiculous it was.
"I'm sorry you lost her." And she was. Because Sarah, who hadn't known Alison for very long at all, wanted nothing more than her happiness.
"You're the only person I can talk to, and you're just another version of me." Sarah couldn't help but feel like she'd won some sort of competition. Alison was dangerous, Sarah learned. She didn't know whether to be terrified of her or pity her.
She decided she was comfortable in both.
It never stopped Alison from lingering in the back of her mind every single day, however.