does cheating and lying is correct??

Do people have ethics every time they cheat? Does cheating is the best way to solve peoples problems? Human Beings tend to lie, tend to cheat, tend to do the bad thing even if its not intentionally. But what i think is that if you cheat and you believe is the correct thing to do then its morally good, because if you believe in something and you do it then is the righ thing to do, but if you are thinking if you cheat or not and you dont decide what to do, then that is not morally good. You have to believe in what you are doing in order to be morally good. However, cheating to your wife and destroying your family isnt ethical, because you have a family to be with and if you cheat and lie and not be honest then why you marry?.
In the other hand we have lies. Lying to others is not ethical, but in many circumsatnces human beings lie because its the only right thing to do in that momento. Lying is not always un-ethical, because sometimes we have to lie in order to not hurt other persons feelings, but at the same time is not moral good because your not being honest with that person, so its not good nor bad, its according in the situation you are.