I think there can be a number of reasons for that. One can be that you are forced to marry a particular guy/girl but you don’t want to marry him/her. Other can be that you get bored from seeing the same person everyday and you’re bored. Whatever may be the reason extra martial affairs are not cool. Yoh break the other person’s trust they had on you. Just sit with your partner and have a conversation it can solve a lot of things.