It's simple

The reason it's so painful when someone disappears is you have to face the fact that the person you loved had probably left you long time before he grabbed his coat and scrammed.

The hard part is realizing that he was lying to you, in some way, before the moment of vanishing. Don't ask yourself what you did wrong or how you could have done it differently. Don't waste your valuable heart and mind trying to figure out why he did what he did. Or thinking back on all the things he said, and wondering what was the truth and what was the lie.