Hi Rhio,
First off, I'm not a mum, but I do work in the domestic abuse field and conflict over child contact is a common feature of abusive relationships.
I can't give you legal advice of course, but I can give you some general advice.
First things first. No more sex with him. If you are limiting contact on the grounds that he is abusive, he will use this as 'evidence' that you are not scared of him and are showing affection towards him.
Secondly - don't have him in the house. If he is picking your son up for contact, either hand him over in a neutral public place, or have a relative hand your son over, or if he must come to the house, he doesn't come inside. Same reason as above.
No more texting now either. If he calls or texts, say 'please contact me through your solicitor if you need to change any plans'. Do not be drawn into conversation as he will then have a chance to make you feel guilty or try and persuade you to get back with him. This will only draw out the situation. If he can be trusted, you could perhaps agree that he can contact you via a family member if this suits you better.
These things are hard to do and will take some work from you, but they will let you take back control of the situation. You mentioned physical abuse, so what I will say is this: if you are frightened that doing any of these things will cause him to try and harm you, you must take steps to protect yourself. Call the police if he starts threatening you or turning up in the night banging on your door. Keep calling every time it happens. If he texts persistently, get some legal advice about obtaining an injunction. Document every conversation you have - even if it goes well. It will make it much easier to explain to your solicitor if you have everything recorded. Consider changing your phone number.
What I will say is this - abusive men do not change. No matter what promises he makes, do not get back into a relationship with him. It is in the best interests of your son to grow up in a calm, safe household. Your ex may be a great dad when he has your son, but a real father would never abuse the mother of his child.
I'm sorry to get all serious on you, but I deal with this every day and I can say with confidence that the more times you forgive him/have sex with him/etc the harder it gets to break away and the longer you will suffer.
Edited to add: if he does produce all your texts in the child contact case, ask your solicitor about having your phone history downloaded. The police have a computer programme which can download every text you have ever sent or received from that phone, even if it is deleted. Your solicitor might know a way to have this done privately. While it won't make the texts you sent go away, it will mean all his texts are evident as well, so it won't look one-sided. Be warned however - I do mean every text, including photos - so if you have anything rude or embarrassing on there they will see it! If it isn't relevant to the case it shouldn't be brought up, but obviously your solicitor would see it when they looked through the records to see what evidence can be used.