I've always thought that there was a distinct difference between Nine's fiercely protective/possessive attitude towards Rose and Ten's more distant perspective. People say Ten was more open with his emotions, but only Nine bared his soul to Rose. He was the one that would have come back for her- no matter what the cost- and then would have been brilliant enough to fix it.
"... there's me." It's moments like these where you realize how Rose completely saved the Doctor. He was in self-destruct mode until this pink and yellow human healed his hearts and taught him to love again. (Love this photo and the commentary here!)