A Mistress, Really?

I haven't seen the film yet, but from what Agatha told me, I don't think I will like it. Geremio has a mistress? I don't understand this alteration because it changes everything about Geremio and Annunziata. Annunziata, and through her pain, Paul dotes on the memory of Geremio, even going to visit the psychic to makes sure he isn't in any pain on the other side. Can this strong connection withhold such a schism as infidelity? I wonder if this would change Annunziata's belief in her husband and strong connection to God. Then again, this all depends on Annunziata being aware of the affair.