I truly believe that when Yoshi mentioned that they would give each other their virginities, Shoshonna suddenly realized that she was in fact running from her problems. She wasn't honest with Yoshi, and so, the closest person to her there, who she could potentially see having a romantic relationship with, didn't actually know her. So, it was then that she felt alone in a foreign place. Noone really knew her. And Yoshi, as much as she liked him, he could never accept her for who she really is, and she knows it. Japan, for her, was like living in a dream world, one she doesn't really truly belong in. I'm sad for her because I think she was in denial, and now reality has hit for her.