L.,
My first thoughts are time and distance. You have to give this time. You've been in a pattern with her for a long time, and now, you're changing that pattern. She doesn't like the result, so she is going to do what she can to draw you back in to the old, comfortable, familiar pattern. Resisting this pull is hard, but over time, and if you put some physical distance between you and your sister, it will get easier.
In all the times past when you've helped your sister, you've done it with the hopes that it would be beneficial to her, that she'd get herself together and not have the same problems on a continuing basis. But that didn't happen, and now you are left grieving for the relationship that you'd hoped you could have with your sister. Despite all your best intentions and help, your sister didn't change. That's not your fault; it's not under your control. It's natural to be sad about that; she's your sister, and you love her. But there is nothing you can do to make her change and deal with her problems, whatever they are, unless she takes those steps herself. It's sad to see a loved on struggle, but you cannot live her life for her. So, some of this is just you coming to terms with that and dealing with the feelings of loss that you're left with.
By giving yourself time to sit with these feelings, recognize them, and put them in perspective, you will come to acceptance. Putting some distance between you and your sister will also help with that because you'll see how good it feels for you to not carry the burden of being responsible for your sister's happiness.
Give yourself the time and space you need. That's how you limit this kind of behavior from affecting you so deeply.
I truly wish you strength with this.
J. F.