I can't imagine how hard this all is for you. I'm so sorry.
My children are much younger, so my only experience with boundaries is on that level, but just as with a toddler, we lay down boundaries for 2 reasons: because we love them and don't want them to grow up miserable because they have never learned that some behaviour is unacceptable, and end up without the tools to deal with real life, and also because our lives cannot be held ransom to the whims of a rampantly demanding child.
I know it is different, and more painful, but just as a small child hates us when we say no, and doesn't understand why at the time, but we stick firm no matter how it pains us to see thier anger and discomfort, because it is the right thing to do for us and them. That's where you are now, he doesn't understand now, but that doesn't mean he won't ever understand, and love and hate can co-exist.
I'm not putting this very well, and I'm not trying to minimise the pain you feel or the difficulty of your situation with the toddler analogy, just trying to say you are doing the right thing for him and you, no matter how painful and no matter whether he understands that right now.