Thank you Crapbag and UsuallyLurking for your kind responses.
The reality is that I can't manage my relationship with my mum. She presents herself as vulnerable and I find myself every time slipping into the habit of supporting her and so really, it's all or nothing.
It's in my nature to always help where I can, but with mum, she needs more energy than I have to give and so usually I find myself really unhappy where I can't eat, sleep and just feel like the world is going to end and find it hard to see a situation where life will be good again not because of things that are happening in my life, but because she wears me down over time and then pushes me until I snap and it's my world that crumbles and I'm the one in the wrong that the family gives no support to, while she plays the victim.
It's very hard and many times in my life when I've really needed family support (as I'm sure is natural for most people to need to have support from their family at points during their lifetime) when because of mum's behaviour and how she's treated me, I've felt like I've had no-one to turn to.
Such as when she was telling me during my lunchbreak while I was 7 monts pregnant and sleeping on her sofa (as my sister had asked her to tell me that I could no longer sleep on her bedroom floor with only a duvet under me) - rather than being able to turn to my Aunt with two spare bedrooms and ask if I could stay with her - mum had told me repeatedly how my aunt could not believe how I was treating my mum and what a bitch I was being - and so I had no-one. In the end, the next door neighbour caught me crying outside one day and let me sleep in her spare room. There was no bed so I bought a blow up mattress. I finally got my own place and moved in the day before I had DS.
And yet, I still take her back and still fall for it every time.
I've had a tough year last year. DS's behaviour became a lot worse as he had two new teachers this year which have been a lot less caring than his teacher last year and so he's been really unsure of where he fits in which is difficult to deal with as he can't process his emotions well and will be really angry and upset about something a fortnight after it happened. Of course, my family has been really supportive. Mum told me that my sister-in-law-to-be was worried when we visited that DS would fall onto the baby and so felt like I was an unwelcome visitor. Bro of course would never say it to me but always via my mum. Similarly when it was my nieces birthday, mum felt it necessary to warn me that DS will have to behave himself while we were at the SIL-TB's grandmother's house in case he broke something - although he means to be naughty and would do it on purpose FFS.
I didn't see her for 8 weeks in 2013 because despite me explaining to her very clearly that DS needs continuity and the pressure that I have been put under by school to do "my bit" to help with his behaviour - she still would undermine what I said. When I would say to her "he's had a bad day at school do not give him chocolate" she would give him some when I couldn't see and tell him not to tell me. Actually having to tell an adult that if they can't behave that they can't see their grandson is just ridiculous.
They'd also invite me round for a family take away evening and then they'd put on a film with a rating far inappropriate for DS but then be all "well this is what we do so if you don't like it don't come" so I stopped going.
I think that NC is going to be a good thing.