I can't give any further advice above which has already been given but am so glad you are feeling stronger and doing the right thing.
As others have said, if you need to ask anything or to seek reassurance at any time, just come here and there will nearly always be someone about to speak to you.
Of course, the whole idea of making the break isn't easy - especially when chances are he'll try to make you feel bad and cause trouble but you need to keep telling yourself that so long as you stick to your guns with this, that one day it will be over and you will have come out the other side feeling so much better - which will of course then also reflect on your son.
No - he - your son, doesn't "deserve" his parents breaking up, but the "togetherness" you have isn't really what being together is all about anyway and I think you know that deep down. What your son does deserve is a happy, self confident mummy and to be able to live in peace. If he hears the aggression and contempt implicit in the c**t word on a regular basis then he doesn't have that now. It doesn't matter that he is too young to know what the words literally means, the horrid tone of it will be enough a) to frighten him and b) plant the seeds in his mind that that is how men treat women.
Please, please, don't let yourself be treated like this any longer. There are real men out there who will treat you with love, respect and consideration but if I were you I'd simply concentrate upon giving yourself and your son the best life you can for the moment, forget about anyone else, and think about yourself for a change.
And don't waste any more time worrying about presents .... I think that worry was a symptom of how you feel - "worthless" - rather than a cause. Once you kick this "man" into touch, you won't need to think about who bought who what - it simply won't matter any more. Who'd want to be part of such a family who've managed to drag up such a revolting man anyway ?
Do see your GP and a solicitor too. There's no shame in seeking help, none at all.
Stay strong ! This will be over one day - bullies like him might try it on but as they get their kicks out of being in control, he won't stick around for long once he sees you mean business.