To answer this question, it all depends on what type of relationship the "I" would be in prior to cheating.
If I was married, I would NOT tell. Telling the person that you love and vow to spend your life with that you have cheated on them is a way of relieving your conscience. That hurt should not be thrust upon your significant other. It should, however, stay with you until the day you die. It should be the cheater who carries the guilt and pain... not the person who was innocent in the equation.
