Cheating is the worst thing any person could ever do, because not only do you betray your partner that has been loyal to you since the day you got together but you also make them feel worthless and not good enough, they start to think that you had a reason to cheat and that reason is because they're flawed and unattractive, so you basically ruin their self-esteem and it will stay that way for a very long time unless someone special comes to their life and convinces them otherwise.
Some of the consequences of cheating are crazy acts of revenge, the person who got cheated on translates their pain and suffering into actions and makes sure to hurt their ex-partner either physically or verbally so they can be just a little bit even.