To be unfaithful means to have a sexual relationship with someone you are not married to or dating, while you are married or dating. Even though you are married or are dating, you can still feel attracted to others. However, it is up to you to choose what to do with these feelings. When you want to be faithful you can choose to move your attention from the person you are attracted to, on to the person you are actually committed to. Unfaithfulness is always destructive in a relationship. It can be hard to forgive unfaithfulness, and it is even more difficult to trust the person who let you down.