Letting go is certainly hard to do even when it deals with people like your BF.
I guess all I can add is how I do it.
I found that I don't have to let go. I just need to get a better hold on myself. What do I want? How do I want it? I don't always get what I want but at least I'm focusing on myself. I know I'm no God. I know I didn't cause it, can't control it and can't cure it.