I loved it!
I think it's a very good backstory, and one that kinda describes what made Jack what he is: tough on the outside, but on the inside he is really a big softie who will do anything to save loved ones.
Again: I loved it.

This was incredibly sweet and touching! I loved the ending, too!

So cute! I love that you gave Jack a sister! It was so sad but I loved the ending! :) Keep writing!