Marty, there are so many people who can empathise with you. It may or may not help right now- but you are SO not on your own.
My ex husband of over twenty years did the same thing to me more than once. I tried for many years to make it ok, but once trust is gone you have nothing (whether you want it that way or not.) That may sound harsh, but it is the cold hard truth.
I have met you and spent a lot of time with you over the HG weekend. YOU DESERVE BETTER THAN THAT! It took me a long time to realise that fact. A lot of people are arseholes, but there are people out there just like you that value trust, honesty and integrity. Do not settle for someone that treats you like a doormat! The last thing you want to contemplate right now is another partner, I know. But sometime one day you will, and there is someone who will treat you much better I am 100% sure of that.
Those facts won't take away the feelings you have in your heart, but the old cliche of time healing wounds is true. The best thing that you can do when you are finished grieving your loss is get out in the world again. I have dragged myself off to places (like HG) when the last thing in the world I wanted was to socialise. I had fun, I laughed and I realised that I could actually enjoy other peoples company despite a broken heart.
It is her sad loss my friend- you have your integrity and your head held high- not all people are pricks, and someone that deserves you will come your way when you are ready.
Best wishes and I really do know how you feel.
