I had a funny feeling your 'last update' wasn't really gonna be your last update.
Seems like another headfark to me bro. This girl obviously likes you and it sounds like her sister likes you too and is trying to act as a sort of matchmaker.
You need to do what is right for you. I'm sure you've tried being friends with an ex before so only you know if it works for you. I personally cannot do it - I need time to move on and letting someone keep you in their life so they don't feel bad, or because they cannot let go is torture. What do you get out of a relationship like that?
Let's say you decide to try and be friends - what do you think will happen? She'll know you still like her and her interest will disappear over time. And where does that leave you 2-3 months down the road?
Don't let her keep you on a string. You have done well up to now so stick to your guns. Tell her you still like her so you cannot be friends right now. Wish her all the best and say you can maybe be friends at some time in the future. But only after you are over her and she is over you.
Then you can walk away holding you head up high, knowing that you are not this girls doormat.
Sure, the games will start again after that but stick with it. Do not show any sign of weakness and be consistent and congruent with your actions. That means no texting her or calling her when the emotions kick in - and they will.
I have to be honest here bro - sounds like this is one mixed-up girl and I would walk away now and save yourself from any more mindgames and hassle.
I feel for you here - I really hope everything works out but I don't think it can right now.
Good luck bro and be strong.