Not sure anyone is saying we are alone in the universe. I am certainly not. The probability of other life is near enough 100%. The chances of us ever meeting any or even knowing for sure is near enough 0%.
This reckons there are 100 million planets in this galaxy with a possibility of life.
http://news.cornell.edu/stories/2014/06/milky-way-may-bear-100-million-life-giving-planets
The vastness of space makes it practically impossible that there is not intelligent life out there. The same vastness also means that we will probably never know for sure.