Lonely doesn't express as well the idea of being alone and sorrowful.

We must do our best for your uncle and aunt.

Your turn to leave us will come, and then Leila will be lonesome." "I don't think she will care as much." Rivers glanced at the strong young face.

"Why do you say that ?" "I don't know, Mr.Rivers.

I--she is more of a child than I am." "That hardly answers my question.