Dean didn't really have much choice, when it came to believing in magic and things that couldn't otherwise be explained. It was part of the job - and now that Lawrence was like the crazy capital of the world, there was even more than just hunting-related magic around. But he didn't see it as a generally good thing - sure, sometimes it could be handy, and sometimes it was neutral, but most of the time it was bad. And most of the time, things that happened to Winchesters were bad, too, or at least were destined to end up that way.
So when Juliet started breathing again when he kissed her, Dean Winchester almost hit the floor.
He hadn't had time to make a deal, though it would be a lie to say the thought hadn't crossed his mind (maybe a long one, if he could get Crowley to go for it, give him thirty years, or something, time to have this life before he paid for it), but he hadn't had time to even put the thought into any sort of a plan, so how was she...
"Jules?" He was staring at her, probably looking about as stable as he was feeling, somewhere between distress and panic and happiness and this isn't real, this can't be real, how could this be real?. He felt sick, but he was happy, but he was terrified this wasn't real. Maybe he was cursed, too. "You were-" He can't say dead, he won't say it. She's not dead. She's looking at him and breathing and smiling and she's okay now...
His hands clutch at her - shoulders, arms, touch her face, settle with one at the join where her neck and jaw meet, the other pushing strands of hair back absently, repeatedly, smoothing them away because he doesn't know how to deal with this, doesn't know what to do now but he knows he didn't think he'd get the chance to see her alive again and he's not letting her out of his sight ever again.
"I love you." When he kisses her again, it's a shaky combination of desperation and joy, but no less intense for the paradoxical nature of the blend.