Huge assumptions there.
How do you know we aren't absolute? Personally I think the human mind may be absolute and exist necessarily... everything else is within the mind. I don't really know what you mean by 'we can't sustain them'?
And something doesn't need to be true to anyone else. You don't even know anybody else exists... all you know of them is the sense data of seeing them, hearing them, etc etc... every other person could also be in your imagination making your own mind the center of everything; and everything else is just within your mind.
Ok, saying God would be absolute in a philosophical discussion :poke-eye:, huge assumption, lol. And my saying you can't sustain your imagination, means you might think of something, but it doesn't keep going, once you stop it's gone (this ties further into, your mortal, therefore could not be absolute).
And now, instead of the original argument over whether thinking something in your head is real, you want to call an audible and try to say everything could be imaginary in our lives, because we would be the center of everything. This wouldn't make it real, unless you were absolute, and if you think you are absolute then why would you be mortal?
That kind of thinking, becomes very Nihilistic, remember this isn't some pseudo forum, I know you guys just registered, there is a point when you need to stay on an argument, promote it with reason, and when it's been concluded, move on. If you change things midway, please at least show what your changing, and state it clearly.