I wish I had money for every time I have answered this type of question here on YA.
In my view anyone who considers that we are the only life in the Universe is being extremely naïve.
When we consider the billions of Galaxies in the Universe, within them the trillions of Stars and the trillions of Planets and Moons orbiting those Stars I am convinced that the Universe is absolutely teeming with life.
Some no more than amoeba but others who are far, far more intelligent than we Humans and far, far more advanced in technology.
Why should Earth be the only Planet capable of supporting life in this vast Universe.
The only thing we have to do is to find this life.
I am of the opinion that our own Milky Way has a great many Planets or Moons capable and probably are supporting different forms of life.
As far as whether we have been found and are being watched is concerned even though I believe there is a great many lifeforms in the Universe, some far more intelligent and technologically advanced I do not feel that we have been discovered by any of that life yet. The reason for this is the vastness of the Universe and the myriad of Galaxies, Stars, Planets and Moons, also the distances apart all these are.
Finding Earth is like finding a single needle in a trillion haystacks and although I believe there is life out there searching for other life in the same way we are I don't believe they have yet found us.
I doubt they have the technology required to travel 10s,100s or even 1000s of light years to reach us anyway.
Therefore my opinion is that we have not had any visits from lifeforms from any part of the Universe.