(i have bpd, as well, btw)

My sister has a very clear boundary on people not entering her room, however, she has trouble understanding why others would be upset with her using their stuff, and why people would want to break her boundary to retrieve the stuff from her room.

Many times she either takes the items without  asking, or, asks but doesn't return the item. She honestly doesn't understand, she's not being malcious.

I have tried to explain this to her, and it always ends in a fight. 

