Hi Julio!
Welcome aboard.

It's great to have you join us, and thank you for sharing a bit of your story with us. You will find many other members here who will be able to understand what you are going through and have gone through in having a family member with BPD.
Can you share what traits you notice in your sister that cause you to suspect BPD? My mom was an uBPD, and one thing I've learned during my time at bpdfamily is that not all BPDs exhibit the same traits, but overall there are many similar behaviors they show. Have you taken a look at the clinical indicators of BPD? I'll include a link here for you to reference:
https://bpdfamily.com/content/borderline-personality-disorder-clinical-overviewIt is a very challenging disorder to deal with. I gather from the things you wrote that you really wish to have a positive relationship with your sister yet you are rather lost in knowing what to do.
I'm sure I've done a lot of things to piss her off, and that she has in the past genuinely wanted my love and connection, but I've been poor with figuring out and communicating and being consistent with boundaries.
Please know that the relationship failure/stress you feel really doesn't have to do with you, but rather with how a BPD is unable to handle most of life and the normal ups and downs of relationships, especially those parts that cause them to feel insecure and rejected. Healthy people can navigate through the waves that come and go, but a BPD cannot.
My goal at this point is to feel secure with myself and my decisions, and to do what I can to try and pave the way for a decent relationship with her down the road.
This is a wonderful goal to have!

Learn about BPD and how you can take care of yourself, first and foremost. Don't feel guilty for doing so because this really is the key to healthiness for you and your relationship with her. Have you ever reached out to a T who understands BPD?
Wools