The error, of course, is that it elides between two meanings of "faith." You trust your wife because you have (one would hope) spent a great deal of time with her and found her to be honest, concerned about your well-being, &c.

Of course, you might at some point come upon evidence that this is not warranted, and in this case the irrationalists might have a point: it may be more wise to use motivated cognition to convince yourself that she is faithful or still in love with you. Othello can be read as an extended argument for avoiding reasonable conclusions if you know that your reactions are not guaranteed to be reasonable.