Andrew! Love it.
My take on this verse. The mention of Jesus’ response to the adulteress brought this to mind. Both are written by John, quoting (by memory) what Jesus spoke. This implies that John is at least likely to have meant the same thing by condemn/condemnation in both stories. “He that believes not is condemned already because he has not believed in the name of the only begotten Son of God.” and “Neither do I condemn you; go and sin no more.”
Now when you take this to Romans; “The end (result) of sin is death,” it begins to make sense (to me, anyway).
What is the condemnation that Jesus does NOT level on the adulteress? Her condemnation (sentence) was death. And sin always does lead to death.
All who continue in sin are doomed to die; but Jesus said to Martha, “I am the Resurrection and the Life. He who is believing in Me, even if he should be dying, shall be living. And everyone who is living and believing in Me, should by no means be dying for the eon. Are you believing this?”(Joh 11:25-26 CLV)
So the one who believes in His name is not under the condemnation, and the condemnation he is not under is death. (note: not eternal torment.) The condemnation HAS to be death, because Jesus is the life and there is no other. Apart/detached from Him, the Vine, we cannot but die. However, we are all in that situation UNTIL we are grafted in to the olive tree. After that, we draw our life from the tree (Jesus is the Tree of Life).
Therefore the one not believing IS condemned, but he can and will escape that condemnation by believing.