Reality as we understand it bears only a passing resemblance to the physical world around us. We have a limited number of imperfect senses to tell us about our environment, which we filter through a mess of cognitive biases, and then store in a faulty memory system. When we step away from the realm of pure mathematics, we fall into a mess of half-baked assumptions made by our ape brains. The reality in which we exist is a mental construct made from abstract categories that loosely align to objective phenomenon.
Definitely. René Descartes, a Latin philosopher said “Cogito ergo sum” which translates to “I think, therefore I am”. Some would argue that this is really all anyone can be sure of in life as the rest is all up to our personal interpretation of what we experience. Terence McKenna had a theory which was that the world itself is made of language. That if we describe the way the world is, for a limited time, in a limited space, it will change and shimmy to fit that description. So when we consider the phrase “Of course it is happening inside your head, Harry, but why on earth should that mean it
Here he was, risking his life for his friend, a friend for whom Ron's whole family had risked their life, but Harry couldn't muster enough emotion for the girl he claimed to love.
Nobody at Hogwarts now knew the truth of what had happened the night that Sirius, Buckbeak, and Pettigrew had vanished except Harry, Ron, Hermione, and Professor Dumbledore. As the end of term approached, Harry heard many different theories about what had really happened, but none of them came close to the truth.
So yes, Ron did know about Harry and Hermione time-traveling.
Ron did try and come back. He regretted leaving the minute he left and as soon as the effects of the Horcruxes wore off, he tried to return back to his friends. The unfortunate thing is, he couldn't.
Of course, it can also be read as suggesting that, even though the reader didn't physically go to Hogwarts, they still experienced it.