It's not so much that he believes her, but he wants to try, for her sake if not for his own. Funny how it's easier to do harder things when it's for someone else and not yourself, right? Jason's known he cares for Cissie since they first met, back in Wonderland, when she showed him unprompted (undeserved, he'd say) kindness without expecting anything in return from him. He's known he's had something of a crush on her at least since the ball, and those feelings only deepened after he became a teenager again and she did what she could to offer the boy he used to be a measure of comfort in a difficult situation. He'd punched those feelings down, though, because he knows that Cissie is much too good for him, and he's already had enough heartbreak in his life. Why screw up a friendship with complications? Nah.

But now ... hell, he'd gone and died again, and she'd mourned him. She's glad he's alive again, and making her even a little bit happy is a worthwhile cause, in Jason's opinion. She's only known him a short time, and she's demonstrated that she cares about him more than people who've known him for much, much longer. She thanks him for coming back, and his arms pull her in just a fraction closer, holding her tightly as the tears return to his eyes.

"How could I stay away?" he asks, softly, and if his voice trembles, he doesn't care. What's important is that he loves her, no matter how that feeling is sorted, and they're together again.