I think it's brilliant to blend non-monogamy and atheism. Having grown up in a religious environment (Southern Baptist even), I am constantly unpacking the pressures of that life.
One thing I've realized of late is that religion encourages conformity to specific expectations that come with specific (and seemingly awful) consequences. If you don't make consistently "right" decisions, then you are damned for the rest of eternity, and, damned means XYZ (fire, pitchforks, etc.).
Monogamy has similar expectations/consequences. If you don't give up your desire to know other people intimately and profess that one other person will answer all of your needs, then you will face defamation and shame at the least. Honesty, it turns out, is not a meaningful part of monogamy as it is societally understood, because to engage in monogamy, you must first be dishonest with yourself (similarly to religion).
Both of these systems (religion/monogamy) seem (but are inadequate) to provide answers to a much harder human experience/skill set. . .being open to the potential for change and embracing a broader litany of potential.
I'm curious as to the experiences of those of you who learned your life philosophy outside of the seeming comfort of religions dictates. How did you (or have you) come to be comfortable with the randomness of possibility and the beauty of "what if"? To embrace all that you might encounter in a given moment rather than focusing on the phantasm of future solutions?