"The end does not justify the means"... always.
It's ironic how some feel they are justified at keeping their wrongdoings a secret for the reason that they are "protecting" their loved ones. Don't they realize that the fact they were able to do something that would hurt the people they love and who loves them in return, implies they don't care the way you thought they did?
I for one am not into tolerating such unfaithfulness. Trust is given wholeheartedly and nobody is excused to break that. No reason is applicable at all. Every time you are about to do something bad, always think of being in another person's shoes. If you are to be done the same thing, what would you feel? How would you react? Nah, perhaps you can't imagine because you are not the victim in the first place. But know that karma exists whether you believe it or not. Maybe not that soon but it will come. So always practice trustworthiness without ever thinking that you can get out of the mess you created yourself. God is watching.