First of all, there are countless universes, galaxies, and stars. To think that Earth could be the only life-sustaining star/planet in the entire cosmos... well, I don't believe it for a second. As for the thought of believing in g-d and that is why we are the only planet with life, even the Vatican has stated that aliens most likely exist because not having other life-sustaining planets would mean that there would be a limit to g-d's power.
It used to be thought that everything revolved around Earth. Now we know differently. Perhaps in the future, we can be more certain about life on other planets...
As for alien or UFO encounters, I've never had any.