If you're doing the caring
This page is not about them. Everything else on this site is written for the person with BPD or for someone trying to understand them — this one assumes you have been carrying something heavy for a long time and nobody has asked how you are.

Where you actually are
Carer strain in this population is high and help-seeking is low. Locate yourself honestly rather than by comparison to someone worse off.
What is actually yours to hold
Tick what you currently believe. The unticked ones are usually where the weight is.
Unlimited availability is not, in fact, available — it is availability until you run out, and the running out is what gets experienced as abandonment. Consistency you can sustain is worth more than intensity you cannot.
Questions carers ask, usually not out loud
All of these are common and almost none of them get said.
Am I allowed to want a break?
Yes, and needing one is not a moral event. A carer who takes a fortnight is more use over a decade than one who does not for five years and then stops entirely.
What support exists for me?
More than most carers claim. Carers' assessments and allowances exist in many systems; carer support groups exist specifically for family of people with personality disorders; and family-focused programmes — a number of services run them — are designed for exactly this. It is worth asking directly rather than assuming nothing applies.
Should I read a book written for them?
The mechanism chapters, yes — recognition changes how you speak to someone. The skills chapters assume the reader is the one dysregulating, so they will read oddly. There is a page for parents and one for partners on this site that cover this.
What if I resent them?
Nearly universal in long caring roles and rarely admitted. Resentment that has nowhere to go leaks into everyday interactions. Somewhere to say it out loud is not a luxury — it is what stops it arriving sideways.
What if I want to stop?
That is a legitimate thing to consider and it deserves a proper conversation rather than a decision made at the end of a bad month. Talking it through with someone outside the situation is the right first step, not a betrayal.
What actually helps them most?
Consistency, calm, validating the feeling without endorsing the behaviour, and not managing their emotional state for them. Almost all of which is easier from someone who is not depleted.