When someone lies to you, it’s because they don’t respect you enough to be honest, and they think you’re too stupid to not know the difference.
When some one lie to you, they can have many reasons to excuse themselves. They blame on the context, on some one or on you.
Actually, the only reason is that they don’t respect you enough to tell you the truth. They are wise enough to understand that when you are deceived, you will be hurt and disappointed. You and that person may never love and trust each other anymore.
They still choose to deceive you because they don’t respect you nor the relationship between you and them.
Or they think that you are too naive to realize their lies. They on one hand, do wrong behind you, on the other hand, they still try to show that they treat you well as if nothing happens.
Thus, when they are not faithful and honest to you, the relationship between you and them is going to a dead end and there is no escape because they no longer respect or appreciate you.