When your spouse has cheated on you they have broken the bond of trust, (not to mention the person's heart) that you both once had and this is extremely serious as it will take a long while before you can ever trust your spouse again. Let them know that! Tell your spouse what is in your heart and how you feel and both of you need to learn good communication skills in order to rectify problems in your marriage. It appears this has not been happening in your marriage. If there is no communication between spouses then one and the other do not know what the problems in the marriage are and thus, cheating may occur by one or both spouses. After explaining if your spouse appears not to understand or does not care to understand how you feel then ask them how they would feel if you had done the same thing to them. If they come back with a flippant answer such as 'Feel free to do so' then kick their butt out the door and separate for awhile to give both of you time to think things over and decide where you want your marriage to go or, if it's time for you to move on with your life without your spouse.