Hi there
Welcome to bpdfamily Living with someone who has BPD can be very challenging and I believe many of our members will be able to relate to the struggle you're going through. I understand your loyalty to your sister and you desire to help her. But at the same time I would also advise you to try to put your own well-being and that of your son first. That may sound or feel like being selfish at first, bu the reality is that you can only help someone if you first take good care of yourself.
Has your sister been officially diagnosed with BPD and do you feel like she in any way acknowledges that there's something wrong with her behavior? You mention that you've been taking care of her for very long, how long has your sister been living with you? And since when did she exhibit BPD-like behaviors, was there always something wrong with her behavior from the very start or did it start at a later moment?
Since your living with her with your 16 month old son, I would encourage you to read some information we have here about boundaries and how to set and enforce them. These are very important skills when dealing with someone who has BPD:
BOUNDARIES: Upholding our values and independence BOUNDARIES: Examples of boundaries