Pretty difficult but wanting to change is a big step. Perhaps therapy to get at the root of that need to lie could help change
My father is a pathological liar. I'm sure there is treatment available out there for him, but the trouble isn't hat he has created this whole fantasy world where everyone else has the problem, not him. Since he will not admit to having an issue, he refuses to seek help to try to fix it.
I dated and then had a child with a pathological liar; the mother of this person was aware of it, told me she tried all kind of counseling and nothing worked. Now I'm raising this child all on my own because of the pyschological stress of dealing with this person. This person also was categorized as being in the range of mental retardation; I suspect that the lying was more a very deficient character flaw, as apparently one of the parents was exactly like this, too. I don't know if you have to attack and confront these problems very early in a child's life or if some serious mind altering therapy needs to occur.
tricky one that,i've known a couple of people like that..really annoying