So tonight I put pen to paper and wrote out what I'd like to say to her. I won't be sending it. But it helped me a little.
I'd love to hear what others would love to say

P.S Mods, I'm not sure whether this is appropriate - if too emotive for the leaving board, please remove.
Dear X,
You know - I knew you weren't perfect. But I loved you. You treated me like a princess and that was good enough for me. I overlooked a lot, things from your past, as I believe you shouldn't judge somebody on their past, but on their present.
I want you to know that I understand in some ways why you ran. You got scared I was going to leave first, that I didn't love you enough. Let there be no doubt - I adored you and worshipped the ground you walked on. I would never have left you. Yes, I emotionally detached a bit at the end due to your crazy mood swings and depression, as well as the constant dramas and negativity. But I overlooked so much, because I loved you.
You're with somebody else now. I wish you could have been honest with me, as I feel I will never know the truth. I hope she is everything you ever wanted, and in some ways I hope this works out for you, as you lost SO much the day you walked away from me. You lost your best friend, your partner, your biggest supporter, and your rock. I would have done anything for you.
I will always wonder what our wedding day would have been like. What dresses would we have worn? What would our wedding reception have been like? I'll never know. You've killed my dream. Our dream.
I wish I understood why you thought I didn't love you... . your stupid self-sabotaging brain... .
I wish I could be the one to wrap you up in my arms and protect you from this world. But I can't. Only you can do that for yourself. You won't find it in your new girlfriend - she cannot fix you.
Just so you know, when I made that commitment to marry you, and you put that ring on my finger, that was it for me. I thought of "us" as every default option, not myself. We were like one person in some ways. You broke my heart when you left, you didn't even give me a chance. It was all about YOU, all about keeping yourself happy. To hell with me, even though we were supposed to be a team!
What makes me saddest is that you're not the sweet girl who was mine. The computer geeky, hoody wearing, shy, innocent and sweet person I met. I'm going to cherish those memories of the early days, put them in a box, and disentangle them from who you are now. Our relationship will remain frozen in time. Maybe that's the best way. It ended pretty much as quickly as it began. So at least I don't have bad memories. I'll always treasure what we had. I'll always think of the sunny days having a picnic in the park, drives in the summer evenings, and time spent with friends. Amazing, picture perfect memories.
And for your information, I wanted us to be reality. I was prepared to work for it. It breaks my heart that you weren't - you ran as soon as we were no longer "perfect". You're going to be very disappointed in life if you always seek perfection.
And I wasn't perfect. I'm so sorry I let you down in the fact that I wasn't perfect, but I'm real. I would have loved you til the day we died, I would have always put you first, I would have looked after you when you were sick. I'm so sorry that wasn't enough - and I mean that - because I wish I could have been that amazing person. But you know what - these people don't exist. You just think they do, until suddenly your view changes. Even though the person was the same person they always were.
I'm sorry I cannot continue to put you first. That's all I ever did. I won't do it anymore. I'm sorry I have to break this promise to you that I made, but it became null and void when you left.
I know that deep down, you're such a good person who's been battered by life. I hope you find every happiness, and fight your demons, because I know you have a beautiful soul.
I will always love you from a distance, I will always love the "you" that I met and planned to marry, and I will always wish that things could have been different.