So compulsive lying is a very complex human problem. It sounds like his lying is not affecting your relationship, but is upsetting to other people. If your friend feels his lying is interfering with his life, and he would like to change, it may be very helpful for him to seek counseling. You need to know that only he can make the effort to change. Little you do will have any effect.
Counseling can help with behavior change and with support as changes are being made.
For you, you have to ask yourself if this is really not a problem to you. If it is now, it will become more so if the relationship continues to develop.