"Okay, I’ll obviously approach Delphine way more logically than that."
"I didn’t want to fall for you. I wasn’t supposed to. But I have."
Those two lines of dialogue gave me feels so I made a thing. Cosima knows that logically, she shouldn’t have feelings for Delphine. And she tells Sarah (mostly to convince herself, I’d wager) that she’s monitoring Delphine and reassures her that she’s got things under control. Cosima wouldn’t fall into bed like Sarah did with Paul. But when Delphine kisses her cheek and her eyes flutter a bit and she can’t wipe an especially dopey grin off her face.. it’s game over. I’d like to think that little exhale as she watches Delphine walk away is a sort of like “Well, shit.”
And when shit hits the fan they both very quickly realize how much they’ve fallen. Cosima is furious because she should have known better. Delphine, well, she just wants to make it right. I don’t think she knew what she was getting into. It’s so simple to blindly agree to something before you meet a person that explodes your entire world open. Which is what Cosima did for her. And what Delphine did for Cosima.