Savannah's smile echoed his in the moment before their lips met. It may have been casual to CJ, but it seemed sincere enough to Savannah. That was, of course, by her definition of sincere. It was one of the things that she found attractive in CJ. The relationship may be casual, but nothing CJ did ever seemed that way to her.
She had had long-term boyfriends who treated her more casually than CJ did. His touches, his kises, and even the way he looked at her made her feel like she mattered. She would not deny her attraction to him, nor would she say her feelings for him were completely physical, but she had accepted the relationship for what it was, because he respected enough to be honest with her.
And so she gave into his kiss, allowing her lips and body to communicate her willingness and openness to him.