Ultimately, we are all alone.  Each of us has relationships with other human beings, but we are still alone in our heads.  Since we have no idea what is beyond the small parts of space that we can locate and search at a distance, it is hard to say that we are the only intelligent species in space.  If we exist, why couldn’t another planet be inhabited with what we would call an intelligent species?  It might be farther away than we can reach, and they may not have technology advanced enough to reach us either.

There is no evidence that we are not alone in the universe, but given the size and complexity of the observable universe, I think it is highly unlikely that there are not other life forms somewhere. The discovery of planets outside the solar system in recent has made it seem even less likely. Whether life that is similar to us exists is to me the real question, but of course it is almost impossible to know that either.

I assume you mean all of us as people since we clearly share it with one another as human beings.

I do not think that it is possible that we are the only intelligent life in the universe.  The universe is simply too big for that to be possible.  They say there are more stars in the universe than grains of sand in the world.  If that's true, how could there not be life somewhere else?