He didn't just want a kiss, he wanted the bloody world. He wanted to sweep this woman off her feet, have a family, a normal life, hell maybe even make her honest somewhere along the way...but he was John soddin' Constantine. It just wasn't in the cards. Of course when she joked about kissing him, she probably had no idea he wanted all of this.
John rarely let it show, but if she'd ever asked him outright he might have answered honestly.
To her.
Instead, he kept that uncharacteristic silence she seemed to be enjoying and reached up for her face with his hands, leaning in to kiss her. And it was like a ship finally losing an anchor--a man like him, you couldn't keep him grounded. No, she was the fucking sea he sailed through never-ending, and that was why they worked. Constantine didn't even try to hide how he felt in that kiss, knowing she'd know what he wasn't saying by how he kissed her now--like she was the only damn thing that had ever mattered.