Remember 'What goes around, comes around' it's not just a phrase but a harsh reality of life. A betrayal relationship doesn't ever last long.
We can't expect happiness by cheating someone. You cannot ever reach a level of mental satisfaction by cheating someone.
Remember if you ever do something bad or betray someone you would have to face the same in the future.
I understand what do you mean. The problem is that reality is not so simple as you wrote: Alice is bad because she was cheating Frank, Mary is bad because she betrayed Alice and Frank is bad because... Because of what?
We were discussing this with Cnut237. There is nothing like objective good and bad. It is just subjective point of view. Thing that can be considered as cheating or betrayal by someone is totally fine for someone else. Who should tell what is and what is not OK?