Strands of Time by Kris Ruhler

All Kallum wants is a peaceful life in Levitor city with the girl of his dreams. He has life all planned out. But after a simulation test unexpectedly leaves him reeling, normal takes a whole different meaning. He loses his guardian and fears he’s turning into his worst nightmare—a Crazy.
Worse than all of this? He finds he’s the cause of the fracture in the aetherium, a stone of vast energy that powers the dome protecting Levitor. Now the threat of invasion from the savages on the outside looms.
What is this aetherium stone bestowed by the Aeternas, an alien race? Who are they? Why did they give the stone in the first place? Are they so benevolent? Probably not. No Levitorian citizens dare to question.
It’s up to Kallum to fix the aetherium. He will have to choose where he belongs and what is really worth sacrificing for the greater good.
Welcome to the Aeterna Chronicles.