I never said we were the only universe. I don't believe we are. And whether we are or not it doesn't matter for the existence of God.
Before "we" thought we were the only planet, "we" thought we were the only continent. And so on. Yet, even in one planet, we are not even the only intelligent life form. If we allow evolution unhinged (probably won't happen because of colonization, but still) other intelligent life forms could evolve elsewhere in our very solar system. And so? It is always you who insist on a parochial view by which, unless God created just one planet with just one intelligent species, then there's no God. That's like saying Steve Jobs, who invented one thing, is an inventor, and Edison, who invented hundreds, is not.