No, a Supreme Being is not necessary, just highly desired by those who want some certainty about the future, some reassurance that his or her life won't just go "pffft!" and that is it. The darkness is scary, so we create the necessity that there be some assurance that this reality had a Divine Purpose, and that we, as ego-centered beings, have believed that the Universe (and certainly the sun), revolves around us alone.
If a Supreme Being never had a Creator, then that same logic can be applied to an Eternal Universe that never had a Creator, but came into being. If one wants to argue "But Who made it come into being", one can apply that same question to a Supreme Being. Speaking of a Creator is only adding another layer to the story, and it's "turtles all the way down." You can keep adding Creators, or just drop that entire thought and it works equally well.
If a Supreme Being never had a Creator, then that same logic can be applied to an Eternal Universe that never had a Creator, but came into being. If one wants to argue "But Who made it come into being", one can apply that same question to a Supreme Being. Speaking of a Creator is only adding another layer to the story, and it's "turtles all the way down." You can keep adding Creators, or just drop that entire thought and it works equally well.
“I've done everything the Bible says — even the stuff that contradicts the other stuff!"— Ned Flanders