We have discovered over 800 earth-like exoplanets orbiting distant star systems, including one at Alpha Centauri, one of our nearest neighbours. Given the frequency of discovery and what we presently know of physics, both empirical evidence and current theory leads scientists to believe there are possibly billions of Earth-like planets in our galaxy alone.
We have met no aliens.
This must mean, therefore, that at least one of the following must be true:
1. Intelligent life has not yet evolved on any other planets, humanity is the first such example of life.
2. Life exists on other planets but has not yet evolved intelligence, or developed the ability to travel to other stars.
3. Intelligent life has existed on other worlds, but does not currently exist. There may be billions of planets, but the average lifespan of a civilization may be just a few thousand years old, or even less. Possibly most intelligent civilizations wipe themselves out before developing spacefaring technology, or they have simply wiped themselves or each other out in war involving spacefaring technology. Either way, no such life currently exists.
4. Intelligent life exists on other planets, but the laws of physics prevent interstellar travel from being viable on any meaningful scale (it would take tens of thousand years using current technology just to reach our nearest neighbour).
5. Intelligent life exists, but chooses not to visit Earth, or is able to cover up any detectable sign of their existence, either alone or in conspiracy with Earth governments.
6. Intelligent life exists, and interstellar travel is possible, but the times and distances are too immense even with enhanced technology to communicate with other worlds (e.g. only four intelligent civilizations exist within the galaxy at the present time, while they can visit nearby worlds in weeks, it would take many hundreds of years to cross the galaxy, intelligent civilizations may therefore never meet).
In all but one of these scenarios, humanity is alone. In all but two of these scenarios, alien life is not even discoverable (although archeological remains are not). Either way you look at it, the universe is a lonely place.