True to her word, Sarah texted Michael every day about new things she was learning in school or funny things that the others did. In turn she asked him about what it was like living with outsiders and he always told her.
The first time his roommates found out who he was texting all the time they immediately assumed she was his girlfriend. At that point he hadn't even known what a girlfriend was so he said she was a friend.
It was the truth. Sarah was his friend. The most appropriate terminology he could find would deem her his best friend. But that was all there was to it.
She didn't seem to know anything about romance. Every time he came back to visit she would smile cheerfully and wave at him but not hug the way Finn and Carmen did even after short separations.