Eh, it's not really a matter of belief with extraterrestrial life. Whether I entertain the possibility seriously or not, I recognize that it is pure idle speculation with no foundation in reality, knowledge, or truth. I'd say it's possible. Maybe probable. I'd also say it is extremely likely that humanity in general has a limited capacity for imagining such things or placing realistic probabilities on it.
It's possible we are the only intelligent life in the universe, but it is a very big place. It's possible also that there are hundreds, even thousands of civilizations as advanced, less advanced, and more advanced than we -- but that, no matter how advanced, they are on isolated, very rare, far-off worlds with no ability to come into contact with one another outside of infinitesimal chance.