I don't really know the details, but when a close friend lied to me, I like to weigh the gravity of it. How does the lie affect me and the friend group? Were they backstabbing me/us to others? That would be hard and would need a thorough discussion to assess our friendship. Then I look at how difficult was it for them to tell the truth. If for example it was them dealing depression and anxiety and lying about being ok, then I would be saddened that they didn't ask me for help. If they were cheating on their partner, I can understand why they wouldn't share it with me or the group. Like in a lot of relationships, I think conversation and understanding is important.