Shannon felt a lot of emotions, not the least of which was relief, when Dean tightened his grip on her and stroked her hair, telling her that he wasn't leaving. Everybody leaves, the niggling voice in the back of her head reminded her. You're a burden. He just pities you. Instead of saying anything right away, she just clung to him, eyes closed and hiding her face from the world around them.
Boone had been right about her all along. She always needed someone to take care of her. Shannon was disgustingly dependent and if it wasn't one person, it was another. When Sam wasn't keeping her warm at night, there was Domeki teaching her to hunt; Dean comforting her and letting her cry. Or the Doctor, keeping her hopes high (until this morning, that was), and if not, then Jay making her smile or Locke helping her forget that everything was awful, if even just for a minute.
She didn't know what to say, because everything that came to mind sounded stupid or needy or both. And she was both of those things, but she didn't need to broadcast it, especially not to Dean. "I'm sorry," was what finally came out and she wasn't even sure what she was sorry for. The shower? The attitude she'd given him? Getting the God-awful pink sweatshirt (which normally she would've long since poked fun of) wet with her tears? ...using his feelings - which she could only assume he had since he'd been denying it - against him to get what she needed? In this case, someone to tell her that they would take care of her and she would be okay; that they wouldn't let anything happen to her. Shannon was sorry for all of those things, she supposed, because he was a good guy and he deserved better than that. But, Shannon couldn't help it. She was just built that way.