I Still Love You (sterek)

So i was reading a sad ass story on archive T.T and i saw this word, eternal. So i thought of this story and some parts are what might happen. Any ways

Derek and Stiles fall in love during Stiles junior year. But during stiles senior year Derek broke it off. Depressed, Stiles disappear for four years. no one knows where he went or why. His father did though, so did Chris Argent. The only people who knew where Stiles disappear off to.
After Four years stiles come back changed. No the same, More scars than smiles. More sadness than happiness. Everyone is over joyed but they have changed. Derek has a new love. Scott and Liam are married. Issac owns a bakery just down the street. Lydia is with Jackson with two beautiful kids.

everything was peaceful,But what happens when the supernatural starts up again. What happens when three men comes to beacon hills to find stiles.
Where was stiles this whole time? where did he go? what exactly happened to him and how did he change so much?