Her family was not a lie. Her father tried to live the church's teachings, and suppressed a vital part of himself -- one he doesn't want to suppress anymore. That doesn't mean he didn't love her mother, that he didn't love his daughter, or that any moment they had as a family was invalid. It means he has been making a horrible, secret sacrifice his entire life.
It was terribly unfair to her mother. But, frankly, it shouldn't change a damn thing about his relationship with his daughter.