In my situation all the guys especially have been telling me to go NC. And I struggled with it so much. Like you, my WAH and I don't have kids. We really have very little reason to stay in contact. And that scares me too. Like if I do NC then maybe we will never talk again.
And I also completely agree with what you said about feeling it is rude not to reply. If you read my thread you'll see I say a lot of the same things as you.
However, I was able to pull off NC for a short while and I think it bothered my H. And it gave me a little feeling of control too.
I told myself I wasn't going to contact him or reply for X number of days or until X date and then I did it. No matter what he said or did I just didn't reply. I told myself, hey, I have a busy fun life and I don't have time to respond. But if I want I can respond later, after X date.
Your communications with your BF are a bit more spread out than mine, but maybe you can set a date as well. Like his bday. Just tell yourself you are busy until then and don't have time to reply to his email. Take the control. And allow yourself to send him a simple happy birthday email if you want to!
However, here is an idea. He would expect you to say happy birthday, right? So why not throw a wrench in his expectations and NOT send him anything. He may wonder why you don't seem to care. Have you moved on and forgotten HE exists?
The guys on my thread tell me over and over that he must think you have moved on in order to wake up. I think their advice is good.
In any case, good luck with the freelance work and your own business. Keep on getting out there and GAL-ing. And come here to vent, that is why we are all here. We get it!
Oh and PS: I know it feels like if you don't reply to him and go NC that you will never speak to him again. But how is that possible? You can always contact him in the future, any time you want!