Everything you are feeling, and everything you have done to try and 'get him back to his senses'. Is completely rational under the circumstances. You have lost your best friend and lover. So as well as going no contact, you need to stop beating yourself up for 'not doing things the right way' because actually, you've somehow still got to where you need to be now, which is realising and starting to accept that he isn't going to change his mind, he isn't going through a phase: he is never coming back.
And that feels like a death, only in some ways worse, because you know he is actually alive, but just as untouchable and unreachable as if he were dead. And so naturally you are grieving. Grieving. And have been for nearly a year. This is natural, because you truly loved this man. And you love him still. Which is again normal. Bad news: You most certainly will probably always love him, even though he treated you so badly. True love never dies: its like energy; it cannot be created or destroyed, it can only convert to something else like hate or derision or scorn. That's why marriages often end so badly!
BUT the intensity of it can fade or lessen to the point that you no longer are hurt by it and can manage to move on with your life and achieve a measure of objectivity. The only way of achieving this is, as you say, going NC with the object of your affection. No calls, no texts, no letters, no hanging around places you may bump into them etc etc.
There are a load of chemical reactions in our bodies and brains involved when we love someone. When we think of them we get a surge in serotonin and good endorphins. That's why those memories of you together on holiday, birthdays, evenings out cause such longing. You go to a place you went together and it brings back a sense of pleasure and then loss when you remember that's it gone. You have to be analytical and start dealing with these feelings by deceiving your brain. The way to do it is by overriding these memories with new ones. Our brain loves stimulus and novel experiences. Go to the places you used to go together on your own or with a friend. It will kill you the first time but the more you go, the less it will hurt. Override those 'together feelings' with new emotions and memories.
Partly what you're feeling is the loss of your identity as you+1=2. For 17 years you haven't just been you. You've been you+1=2. Now a part of your identity has vanished and you feel lost and alone and empty. Suddenly it's just you.
In our society being on your own is really not looked upon well, but it is very important to do things on your own. I don't just mean with friends. Ask yourself, how long ago was it that you dined out on your own? Went cinema on your own? Went to a play, or an exhibition or museum on your own? When you have made such a large part of your identity dependent on someone else, of course it makes it harder to recover from the loss. So when you feel stronger try doing one or two of those things from the list, and you will do two things: 1. Strengthen your sense of self and come to a greater realisation of your own likes and dislikes and strengths (because in a relationship you always compromise). 2. Open yourself up to new and good opportunities, other loves even, when you're ready. Gradually you'll come to see that there are some upsides to being single, to not having to share, to getting to know yourself again.
You really are a lovely person with a big heart, or you wouldn't care about your ex this much. In addition to going no contact, if you make small steps to move forward from this relationship, good things will come. Read all the posts in this thread again anytime you feel yourself weakening and reaching for the phone. I also recommend the Samaritans; they will listen to you repeating yourself as often as you like and I promise you they have heard it all before.
Don't be surprised or frustrated if you find it still hurts months from now. Or you find yourself suddenly crying out of the blue. It is entirely natural, and as I said everyone is different. Tell yourself: I'm having a bad day, but I lost someone important in my life, so that's natural, I know I'll feel better one day'. Then do something to distract your mind. Any form of voluntary work is also great because you mix with like-minded people and concentrate on other people's problems.
Your ex will sorely regret what he has thrown away, maybe years from now, but by then you won't care. Because you will have learned to value yourself so much more than he ever did. Take your life back from him! Good things (and better friends, and potential husbands) are around the corner. But you cannot wait for them to come to you. You have to make a step towards it, and then the rest will follow. This is one of the most difficult things you will ever do but you can achieve it. You really will. It hurts like hell but one day you'll realise it hurts less. It really will.