BBJ...I don't know if I am projecting my sitch onto yours but your h sounds so much like mine it's not funny.
I think you need to seriously consider the following:
If he was on a business trip then he was likely all about business ie one task at a time, and concentrating on his job, concentrating on the people he is working with. Making sure he can provide for his family by doing a good job.
It is possible that because he was on a business trip that he hasn't read your email. He may have lots of stuff already swirling around in his head that he wants to think through.
What was the subject line of the email? If it even slightly indicated something emotional/deep he may have avoided reading it until he gets some 'proper' down time (when that will be, who knows, and trust me that is humungously frustrating from us girls point of view).
He may have flicked through the email, realised it's a serious one and again, be leaving it till he has some proper time to deal with it. He may sense that you are freaking out a little and in all likelihood, he probably IS taking your temperature when he txts/calls.
I think you need to give him one last chance to read and respond. Once he is back home while you can't control what he does, you can be more aware of the environment that he is in (he's living with you isn't he?) and perhaps see a little more clearly when he can deal with the letter.
I am soooo much putting myself in your shoes. I think I am going to need to do something similar to your letter soon and I'm scared.
** Purple
As soon as you trust yourself you will know how to live. Goethe