I have no easy answers, but I really feel for you and want to reach out. Your Fiancée will never really get over it, maybe learn to live with all the guilt she will feel. However, sometimes that even does feel like enough reason .....
I hope you can stay safe, what helplines or suicide prevention phone numbers are in your a Area? They will always be pleased to listen and support. I have had a it of help from the British Samaritans, they will stay with me even when I can't speak and they have helped me when I have thoughts like the way you feel now.
Wishing and praying that you can find some hope. You will be missed.