Sorry to hear the news I would be the same as you, feeling a little lost, but 70MPH and a tunnel. You both came out ok.. Thats the important thing, I'm sure if you had lost a limb or something you would feel worse of or even worse if your fiancée wasn't ok, then you would feel some sort of guilt.
TBH whats happened has happened and nothing I say will help. But end the end of the day get your mind straight as your can and see you have some options.
1. How much the insurance will give you if you keep the car, replace the shell (kaan has one) and build something better and let your mind run wild.
2. How much the insurance will give you if you write it off and buy something completely different but as good
or
3. Same as option 1 but break down and sell for parts.
Personally option 1 is the one I'd go for because the time your done, stand back and you may think "My car is better than ever, and it wouldn't have happened if it wasn't for that unlucky day"
But I try and think glass 1/2 full and all that..
good luck with it all bud...