It is very difficult for a liar to change, even more so as an adult, I say this from experience, I have a close relative who's middle name is Mentira and he never changes, I hope I am wrong with this person you mention.
After a lie is discovered, the person is angry to be discovered and others will hardly trust him again, but as you say, the problem lies in that person because yours lives go on, it will be on his conscience.
I believe that this person did not have it planned from the beginning, but lied the first time and created a bigger and bigger monster. Evidently he has affected himself, I hope he repents and can start again, but we already know that trust that is lost hardly ever comes back...