I believe its nieve to think we are the only ones. We may never prove extraterrestrial beings exist but, we do, and that's proof positive it possible.
Scientist now believe the building blocks for life could have come to our planet on meteorites. So you could argue, why couldn't it happen somewhere else.
https://en.wikipedia.org/wiki/Panspermia
Yes that could really be a way of life moving in space. I also believe that life could have formed somewhere else and also already disappeared too...who knows!
13 billion years is a long time. Has to have happen!