If he is IC I can assume you are planning to R. If so I would suggest not sending it as it sounds like he (in quite an insensitive way) is trying to reach out to you. So if you’re serious about R, I have reworded your response to be less antagonistic.
"I don't think you get it at all”
= “I don’t feel as though you understand how I feel right now”
“The man I loved, whether or not he ever existed, is dead”
= “I feel so sad that you seem like a stranger to me”
“I gave everything to and for him, and now he is just ... gone”
= “I feel like I have given all of myself to you and now its lost”
“I am grieving this loss alone”
“Meanwhile, I am living this life with a man who sometimes looks and acts like my love, but isn't”
“I don't even know you”
= “I feel like I don’t know you anymore”
“The current boundaries on touching me are this: don't”
= “I am not ready for you to touch me”
“The kids need reassurance right now and they will always get it”
= “I find comfort in hugging the kids and reassuring them, I am always there for them”
“I don’t feel as though you understand how I feel right now. I feel so sad that you seem like a stranger to me. I feel like I have given all of myself to you and now its lost. I am grieving this loss alone, meanwhile, I feel like I am living this life with a man who sometimes looks and acts like my love, but isn't. I feel like I don’t know you anymore. I am not ready for you to touch me. I find comfort in hugging the kids and reassuring them, I am always there for them”
Hopefully it conveys how you're feeling, but retains some dialogue that isn't confrontational.