I'm having trouble grasping the "how." If you've done it, were they written? Like a contract or rulebook? Did you verbally dictate them? Did you collaboratively negotiate them? How did enforcing them go? Is it sustainable?
The "how" of boundaries is a great question, because I get where you're coming from -- if boundaries are just a list of rules for the pwBPD, then that doesn't sound like a very rational solution. Or, if it did work, none of us would be here

Boundaries are for you.
That, in a nutshell.
A common pop culture misconception about boundaries is that they are us finally standing up to the person and saying "you can't do that to me any more", and if we're just... I don't know, convincing enough, loud enough, airtight enough, etc, then through sheer force and white knuckling, the person will stop doing XYZ.
That's very different from
true boundaries.
A real boundary is a rule for yourself / your own life, set by you, related to your own abilities and limitations as a human being (what you can do, what you can't do, what you will be around, what you won't be around).
A real boundary does not require anyone else's cooperation, agreement, understanding, or participation... fortunately! It doesn't require announcing it, explaining it, verbalizing it, or spelling it out. A true boundary is a decision you make about your own life and that decision could even be entirely within your own mind.
The moment we start trying to figure out how to make our pwBPD adhere to our boundary is the moment we aren't actually talking about real boundaries. We might be talking about preferences, or desires, or wishes, or requests, or demands, which are all fine, but none of those are boundaries.
To pull from your post, we could use cheating/infidelity as an example.
A common/pop-culture dynamic is something like:
Partner A: don't you dare cheat on me, I won't tolerate it! (thinking that's a boundary)
Partner B: cheats
Partner A: I told you not to cheat on me! Don't you dare do it again! (stays in the relationship)
Partner B: cheats again
Partner A: I just don't get how to make my partner respect my boundary
Telling someone else what to do, or what not to do, isn't a boundary. Trying to make someone else stick to my demand/request/wish is an exercise in futility, whether that person has BPD or not.
We don't control anyone else.The only person we have 100% control over is ourselves, and we are in the driver's seat for what we choose to allow into our lives, and what we decide we can handle (or not). We have to be OK, though, with the natural fallout of having boundaries to protect ourselves. Having boundaries doesn't mean other people won't be hurtful, irrational, damaging, or insensitive, and having boundaries doesn't mean I won't experience loss in my life. Having boundaries is more like having an umbrella on a rainy day. Umbrellas don't make the rain stop... but umbrellas keep me from getting wet, if I choose to have an umbrella in my life. I may mourn the loss of being able to be outside and enjoy a dry day without an umbrella -- there is still loss -- but I am protected from the rain. The rain can do what it wants, and while I grieve not having a dry day, I am not getting wet.
Going back to the cheating example, a "true boundary" version might be more like:
Partner A: I am able to stay in a monogamous relationship. I am not able to stay in a relationship where there is cheating, or where cheating happens and then there is no therapy together.
Partner B: cheats
Partner A: I am not able to stay in this relationship if there is cheating, and then no therapy. I'll set up a therapy appointment for us for Day/Time, please feel free to come
Partner B: doesn't attend
Partner A: I'm saddened to be ending this relationship. I wish it were different.
I respect myself enough to follow my own boundariesBoundaries are about us respecting ourselves, and articulating to ourselves what our values are. It can be very freeing to realize that we don't have to make anyone do anything, or "give consequences" to anyone about anything... we just need to have our own inner strength to know what we are OK with, and then respect ourselves enough to follow our own boundaries/values.
The only person who can "break" or "disrespect" our boundaries is... ourselves.
Always a great topic, thanks for bringing it up. And do check out our workshop on
Boundaries and Values if you haven't already. I'd be curious to hear your thoughts on it, especially this post, which is so helpful that I'll excerpt the whole thing:
Values, boundaries, and boundary defense are a commitment to myself, not an attempt to force change or control another person.
An important aspect of "boundaries" is that it sometimes takes some effort to grasp is the idea that values are a commitment to myself - not an attempt to force change or control another person.
The struggles of defending (setting) boundaries is often an issue that overlaps greatly with co-dependent tendencies or not having healthy relationship practices. Many people with codependent tendencies lean toward "knowing" well what other people need to do, but struggle greatly to re-focus their attention onto themselves. When the focus goes back on the self, some people struggle to know who they are, what they want, or to take responsibility for how to get it.
So, the quandary can be - "I want this, and I want it from/with a certain person". What we want may be attainable in a relationship with the desired person, or it may not. Part of being responsible for our own well being is accepting this.
Values/boundaries, in practice, is a statement about one's self. So, if we consider the codependent tendency, early in the process of going from an unhealthy pattern to a healthy pattern - early in the process, we might tend to focus on the behavior of others as the solution (e.g. If so-and-so would do this,THEN I would be OK). So early boundary defense attempts can look like "I'm going to do xyz so that my SO/parent will do this". This is not living a value or defending a boundary. Instead, it is really an attempt to control the behavior of another person. The way to check this is to consider your motivation. Are we, in our attempt to defend a boundary, trying to change the behavior of another, or just stating what we are willing to do/not do? If we are trying to change another what we are doing is really an attempt to control or get what we not and this is not healthy.
Values/boundaries are about knowing who we are and what we will choose to participate in. So, a boundary looks more like, "I will choose to participate in abc ... .I will not participate in xwy". There is no statement in this "values/boundary" about what someone else needs to do, only about the self. Boundaries require a sense of personal responsibility. My well being is my responsibility, not the result of someone else's behavior.
Boundaries can be tricky to defend, especially with someone we've been in a patterned relationship with. Seeking feedback about our boundaries can be a great way to get new ideas for implementing boundaries.
M.