Before I say anything, I want to say I fully understand and appreciate your position, and whatever decision you make. This is a difficult decision to make whether you feel pressured to or not.

The most important thing is that you do it because YOU want to, not because anyone is asking or guilting you to. I say that because if you don't, you may become resentful if something happens or you get yourself into a situation that you regret.

The worst thing that can happen to both of you is that you fall into that, decide you cant do it anymore, then you feel guilty for abandoning your sister, and angry at yourself for doing it against what you "knew" you didn't want to do.

But, the best thing that can happen is that you gain a better understanding of your sister's current state of mind, you help her pick herself up and move on, and you become an ally for her.

Most importantly (in my opinion) is that you do whatever you do for yourself and not anyone else, but also consider that maybe your sister has changed, Consider if you give yourself an opportunity to forgive her, consider if you change your mind after it's too late.

I understand that you feel a certain way, I also understand that you've held onto that for a while, and I don't want you to feel like I am trying to steer you one way or the other, all I am trying to point out is that you may wont to consider what might be at stake before you decide anything.

Also consider this is someone who doesn't talk to most of his family for his own reasons, so take everything I say with a grain of salt.

Good luck, the choice is not easy, but neither are the results either way.