One explanation of the Fermi paradox is the zoo hypothesis. It's admittedly a freaky situation to consider, but here it is: aliens know we earthlings are here, but they're purposely avoiding contact with us, opting to study us from afar instead. This hypothesized answer to the Fermi Paradox was proposed by MIT astronomer John A. Ball in 1973. It's named the zoo hypothesis because it suggests that life on Earth is just like an animal at the zoo—look, but don't touch! Ball suggests that maybe alien civilizations are advanced enough to know not to influence our primitive society, or not to get involved with other intelligent lifeforms (the Prime Directive, anybody?).
A more popular answer to the Fermi Paradox is that alien life is still very primitive, or has already come and gone. At this point, it's really anyone's guess. These videos may help you consider the possibilities of alien lifeforms, and where, how, and if they exist.