Wow Julia - Straight forward and to the point. GREAT!! I think this will be a great relief to have off your shoulders. It is horrible knowing that he is living with this 'temporary replacement' but it should be a relief to know the truth and not just keep wondering and assuming.
You are very courageous and strong to send this. No matter what the outcome you are going to be fine and be able to get on with your life whether it will be a step towards reconciliation or a leap towards a new life all together.
I am sending you positive thoughts and ((((hugs))))!!! Good Luck!!