Why is my boyfriend a Pathological liar?

He is always lying to people. Trying to cheat them, constantly. He always has to be good at everything. His parents make him do EVERYTHING. They are so needy and nosey, they ring everyday to see what jobs he has to do. he works for them and his Aunty. How can I stop him from lying, I know when he is lying so he doesn't do it to me cause I have caught him out oo mayn times, but he still does it to everyone else. Please let me know what steps I have to take to get him out of it, we have a 7 week old son together and I dont want him promising the world to him and hurting our son or him turning out like his father.