The Blank Page

I have made an outline of what I want to include in my memoir, but I am having trouble finding a starting part. I know I have heard a thousand times to just jump into the story, that it doesn't matter what part of the book you write first, but I feel like the beginning will set the tone for the whole book, and I just can't find that yet. I've been reading through my old journals and I came across a letter that my ex-husband wrote to me shortly after we parted, back when he still loved me. Needless to say, I can't stop sobbing now. Going back into this is so hard, why am I doing this to myself? Well, I know why. I need closure, if you can possibly have closure from something like that. I'm praying the right words can come out of me to do the story justice. Some people say I am a good writer, but I fail to see it. I seem to make an awful muck of things when I try to write.