Why did you pick me..?

After Hermione found out Ron had cheated on her and gone back to lavender she had gone to the library to let her emotions go thinking she was alone she was not. Draco Malfoy was there and asked her what was wrong she explained and after a while of talking they put aside there differences and became friends. Meanwhile Draco Malfoy had to pick who he wanted to marry picking between Astoria greengrass (the supposed pure blood heir) or Hermione granger (the mud blood) Draco picks Hermione and she always asks why but he never tells her [not yet at least]