If you look closely, you can see the difference in their reaction to this gentle gesture.
Brittany is sort of blissful, happy, smiling contently and displaying the feeling of being just that hint of chirpy. Her head nudge backwards at the end indicates her relaxing and you can see her lips moving together for a humming, happy, relaxed sound.
Santana, on the other hand, is seeping with repressed passion and emotion. She hovers her open, wanting mouth closely over Brittany’s jaw, holding herself back as she keeps the distance while theres a hint of an adjusted face tilt and the open mouthed haughty breathing in of Brittany’s smell visibly longs to create contact as her lower lip shivers for a split second, nudging closer to the upper lip in anticipation of capturing Brittany between them but being denied to do so. Santana’s lightly closed eyes with her highly pulled eyebrows and the hint of a longing smile with the breathing speaks of the depth of emotion Santana is truly trying to hide and control herself from in this very moment. The control is visible in the distance she keeps that is in contrast with what her mouth seems to want, coupled with highly arched and controlled eyebrows as well as the rigidness of where cheek and the corner of Santana’s mouth meet, like holding back emotion she can probably feel like bile building up in her mouth. And all she can do to hold herself together is to keep that distance, close her eyes and compose herself before she breathes in the woman she loves.