Is an angel still guarding the Garden of Eden?

No. Leon R. Kass (The Beginning of Wisdom: Reading Genesis) says we can learn most from the story of the Garden of Eden by regarding it as a mythical yet realistic portrait of permanent truths about our humanity, rather than as a historical yet idealised portrait of a blissful existence once enjoyed but now lost. What he is telling us is that Adam and Eve did not really live, there was no Tree of the Knowledge of Good and Evil, no Tree of Life that would have granted Adam and Eve immortality, and no cherubim.