It's very realistic as far as how one little thing can change everything else and drastically alter your future. Not to give too much away but the little girl and himself get mollested by her dad as a child which screws her up bigtime. His first jump back he tells the dad to never do that again or he'll kill him. The dad freaks out and agrees and never touches her.
The result was that her life was perfect. She was a preppy, he ended up being semi-rich and they were in love with each other and everything was as perfect as it could be. But because he did that the dad molested the crap out of her brother...saved it all up for him. This turned him into a major criminal and he screwed up their chances of being together.
Very well done and not too sci-fiyee. Very realistic.
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For what it's worth.