1. Because he trusted her enough to spill his secret to her, even after she was a bitch to his sister.
2. Because when Serena left, they were all each other had.
3. Because she's a bulimic and his suicidal; they need each other.
4. Because they understand how hard it is to live in the Upper East Side.
5. Because they are the only ones who bring out the best in Chuck.
6. Because she dared Little J to "jail break Eric," yet she was the one who did all the dirty work.
7. Because she figured she owed him one, and Blair never owes anyone anything.
8. Because she told him to call her.
9. Because she "actually care[s] about" him.
10. Because she would sacrifice a good take down to protect him.
11. Because he gave her the green light to "go ahead and do it."
12. Because if Serena is her sister, than Eric is Blair's little brother.