Here is where you might have a problem, though. Most couples don't discuss this issue in great detail. They may express to the other that cheating or infidelity is not acceptable but they do not define what constitutes cheating or infidelity in their minds.
I suggest you sit down and have a discussion with your spouse and you both come to an agreement about what is appropriate and inappropriate behavior. It won't be an easy discussion, especially since his view differs from your view on the subject. He or she may find it hard to view from your perspective or he or she may feel that you are over-reacting. Regardless of how your partner responds when you share your feelings, they are your feelings and you may have to learn to live with the fact that they aren't going to validate them and change their behavior.
You can't force someone to adopt the same viewpoint but you can express the hurt caused by their behavior.