A few years ago I lost someone dear to me tragically. It broke my heart and left me feeling like I should have been able to stop it.
I am so sorry to hear about that. It is very hard to lose a loved one but treasure the memories of that person, especially the good memories. 
It's really hard. She killed herself. I feel like I failed her.
Oh dear, I can only imagine please stop blaming yourself. I feel your pain.