If you fight as much as you say you do, I can't imagine you wanting to break up will come as the world's biggest shocker to him. I, like RT Wolf, absolve you of the pain that you will cause.
It's gonna hurt no matter how you slice it, so use a sharp knife. If you feel the way you do for sure, my advice is get out sooner, because later will come before you know it. And it will hurt more the longer you wait. Trust me.
Here's a hint: even if you are wrong, and breaking up just happens to be The World's Biggest Mistake, you'll both be fine with a little time and gentle patience. Maybe you'll get together some time further down the road...who knows? Open yourself to possibility. I personally don't believe in The World's Biggest Mistake, anyway. There is no wrong answer, as long as you promise to grow from whatever you decide, (and hope the best for him, too.)