My sister hates me. I just don't know what to do and I feel so sad. She's 22 and I'm 25, and she's still living at home with my parents. We have never been close, as children we argued literally all of the time, but the environment that we grew up in had a lot to do with that - my parents basically hate each other, but have stayed together for one reason and another, and so growing up we were always very aware of the tensions between them and a lot of in rubbed off on to us. My mum would tell us both daily how much she hated my dad and it really affected both of us.
But a couple of years ago I got married and during the lead up to my wedding I became much closer with my sister, we talked properly for the first time and actually started to build a proper sisterly relationship - in fact she walked me down the aisle, which was something I never would have seen happening. Then about six months after my wedding she went on holiday with my cousin for two weeks and when they came back they'd completely fallen out - it had been the holiday from hell for both of them, (they're still not speaking now and in all honesty I doubt they ever will speak again). My cousin then told me about my sister's appalling behaviour on the holiday which I kept to myself, until my mum made a remark one day about how awful my cousin had behaved. I know I shouldn't have said anything but I couldn't help but remind her that there are two sides to every story and then I told her some of the things my sister had been up to. The next thing I know my mum has told my sister and it's like a war's broken out. However, after I apologised sincerely my sister accepted my apology and said that that was the end of the matter. Since then we've been fine, we've hardly seen each other but then that's because I don't live at home and we're both really busy but we'd talk online etc. However, this Christmas (6 months later), my sister sent me literally a barrage of texts telling me that she was basically disowning me - she wants nothing further to do with me, no form of relationship whatsoever, that she never wants to see me again. She said she has no happy memories of us together as children, that her childhood was ruined because of me and our parents and that she's never been happy. She said that when she moves out of the family home in June she won't be having anything to do with any of us ever again and that I have always been the favourite and that she hates me for it. The texts literally came out of no where, because the day before she's actually gotten engaged and asked me if I would be her bridesmaid!! When I asked her where it had all come from she just said ever since the problem with my cousin she's basically hated me, basically she's been stewwing over it even though she told me she'd accepted my apology. I just kept apologising and I kept trying to call her but she wouldn't answer my calls and the last message she sent me was that she will speak to me when she has to to be civil but she wants nothing more to do with me. This was at Christmas and today I noticed she was online so I asked her if she was ok and if we could talk and she just sent me another string of spiteful messages and then went off line.
I have no idea what to do, I know that what I did by telling my mum some of the things that my cousin had said was completely wrong, and I have apologised again and again and again for that. There is more to this problem than that - she's blaming me for having an unhappy childhood and being treated like the favourite even though I don't think I have been. What else can I do? I know her, and I know she means this, she's very stubborn and once she's decided something there's no going back - I am so worried she'll never speak to me again. The last thing she said was just because we're related it doesn't mean I have to like you.
I can't stop crying and I can't sleep properly either, I just feel so sad all of the time. Any advice would be much appreciated.