It's a bit of a wistfull look to me. She realizes Takun has other people and things in his life than her. She might be a tad afraid that he will leave her. Maybe she wishes she could be as close to him as those people.
"Certaintaly" it's hard to say anything about her feelings, idk how explain how i feel when I see her face doing that expression. Is like "poor boy she don't want nothing with you" and "Why you're so sad?"