It sounds to me like you might have survivor's guilt, Lark.

I went through something similar when a friend of mine died. I didn't find out she passed until later, and I felt bad for a lot of the things that went unsaid and unresolved.

In my experience, it helps to write down what I would say to the person in a letter and then burn it. Let it all go.

Hope you find some relief.

--Killian