I don't think the ending let him off. I spent nearly all the episode getting angry because I thought they were making it look like she was leading him on and so blaming it on her. But in the end you saw what a twisted user he was. Quite chilling.
She was normal bolshy teenage girl who thought she knew it all. It's his responsibility to keep his hands off her. I also think it was good that she looked so young and that he clearly knew her age, so there could be no ambiguity.
In many ways she was more mature than him in that she had serious thoughts and the capacity to love and feel. It's just that he manipulated her. He's stunted.
He lived in a fantasy - he'll never make it as a superstar DJ, he's running away with a rucksack and a car that he probably doesn't even have enough money to put petrol in.
He'll get another job but he's a failure. Ruby pointed that out right at the beginning when she teased him for not being much of a DJ if he was still working as a mechanic for her dad.
He didn't have the capacity to relate to other people. He didn't even truly like anyone. His life was about what he wanted. That is not going to end happily but someone like him will twist it in his head so it's great because it's too scary to face what a shit you are.
The only upbeat part of the ending is that Ruby will probably get over it. Her dad loves her - even though he's flawed. He wasn't angry or jealous in that last moment. He was just comforting his child.
I'm not diminishing what happened to her and others like her, but we all meet nasty bastards and get burned - some more than others. But there's no reason why someone like Ruby should let him ruin her life.