Inabadplace, I havent been in this situation but the only thing I can say is you need to separate yourself and look from outside. if your child was with a man/woman who spoke to them that way and didn't care for them what would you think? What would you feel? What would you advise them? If they were allowing your grandchild to witness and be dealt with in that way what would you advise?
Now apply that to yourself, and let it give you strength. bed your dc down at your mums to be out of the way, tell your mum your plans, go home and simply tell him you want to split, give him a written letter of why and walk away. Then it's just a case of going through the practical logistics of the split once you are out.
It may "seem" like it will be a bolt from the blue for him and that he "deserves" more but in reality you are both in the relationship and I sincerely doubt he has no clue what he is doing and how you feel so it will not in fact be a shock apart from the fact you are still strong enough and not browbeaten enough to walk away.