Today's gonna be bad..

My fiancé had an ex fiancé die on this day a few years back. She had a seizure, fell out, and hit her head wrong. He feels like it's his fault that she's dead because today is also his brother's birthday. He was supposed to hangout with her that day, but spent time with his brother instead. 
I want to be there for him, but I don't know how to even begin to support him. He still loves her, and (I know I shouldn't) I resent him for that. Thinking about it too much makes me have a panic attack. I'm trying to be a good fiancé.. But I don't know how to act at this point.