Cheating is a destructive act that has caused many relationships to end, and the reasons given for cheating are numerous. If you are mature enough to be in a relationship then you should be adult enough to be honest about your needs and communicate any relationship problems with your partner instead of looking for gratification somewhere else. A relationship is not a test, and cheating only deprives you of the opportunity for a healthy relationship that gets stronger over time. Instead of focusing your energy and attention outside of your relationship these should be on improving things with your partner. If you no longer want to be in the relationship then you owe it to your partner to let them know this instead of being secretive and deceptive while pretending that the relationship is fine.
A good relationship involves trust, respect, and common courtesy on the part of both people. Cheating causes a breakdown of trust, and many relationships never recover from this type of betrayal. Cheating on a test is usually undertaken in order to pass the test, but in a relationship this type of activity will only lead to additional problems and issues in a relationship and make it less likely that the couple will survive the emotional turmoil. Be honest about your feelings, even if they change over time, and don't stray. It is better to cause someone pain by being honest than it is to lie and sneak around if the relationship is dead, or to stay focused on making things better with your partner if there are still feelings.