I had given my second husband a couple of "early warning signal" comments to the effect that I was about at the end of my rope, and that I would be leaving shortly if things did not change. When the time came, I just got my stuff and announced I was leaving. I had already gathered up my most important stuff and stashed it at a friend's house, just in case he took it into his head to destroy anything of mine (he didn't--and I really didn't think he would--but better safe than sorry).
I would keep it as low key and brief as possible. Anything bigger or more involved suggests that the matter is up for discussion. It isn't. Tell him ONLY what he needs to know, nothing more. Don't share your hurt, your anger, or anything else. If you ever feel the need to have that kind of conversation, save it until the emotions are settled down. IOW, just the facts, ma'am.