Nihilism, in the sense of not believing in God, any purpose of life, any absolute truth, or life after death; is a subset of Atheism: all Nihilists are atheists; but not all Atheists are necessarily Nihilists.
For example, the Buddha and Lao Tsu, were atheist, but believed in Absolute Truth i.e., they were Mystics
I was atheist at an realty age. Became nihilist in college reading Shakespeare, Camus, and Neitzsche. Subsequently, I became convinced that Absolute Truth not only existed, but is the core of everyone's identity and all religion, as understood and mystically experienced by the founders of all religions
The absolute truth and purpose is Jesus Christ. There is one book. The bible and many different links to that book. There an understanding of the book, and close to home is the insight and facts of the biblical matter. No faith is addressing sin. Which is important to deal with for the welfare of society and personally.