Cloud did actually lighten up after finding out the truth about his past. It was only because of his constant confusion and the fact he was being used like a puppet that made him so unemotional.

As for Tifa, she was fairly heroic standing by Cloud despite all the lies he told and having to remain quiet for fear of what finding out the truth would do to Cloud. Of course she is still a terrorist, so that undermines just how heroic she is.