Asking if I believe in aliens is the same as asking if I believe in trees. Or cars.
Believe in them?

I know that they exist, for sure. I cannot possibly understand how somebody can honestly think that earth is the only inhabited planet in the universe. That is pure arrogance. The math alone may as well prove that aliens exist.
How many galaxies are there? Millions? Billions? And in those galaxies, how many suns, just like ours, making up solar systems, like ours?

It's inevitable. Yes, they're out there.