the questions around why I got divorced occasionally come up (some seem curious)
Something you can say, to run with what you've mentioned is: "They say it takes two to tango and while I can explain to myself what happened, I'm still trying to distill the takeaways in way that others can easily make sense of. I guess what I can say is that I learned a lot about myself from that relationship."
Part of what you're asking is how to have boundaries in conversations that can lead to intimate moments. Using language to go slow is one way to apply brakes if you are the type of person who has a hard time with boundaries.
I don't know whether to mention or how to describe what it's like to be in a relationship with a pwBPD.
Start fresh. Talk about qualities you're working on in yourself to help you be successful in the next relationship. You learned about your values, your limits, what is required to be in a healthy, loving relationship.
I don't want anyone to think I gave up easily on my commitment (was married 5 1/2 years)
This is an opportunity to demonstrate how to others how to treat you. If you don't want to feel judged about something that is so private and meaningful, you can't judge yourself
If it comes up, and you feel comfortable discussing, why not say, "I take marriage seriously, so going through a divorce was among the most painful, sobering things I've experienced."
I also don't want them to think I'm talking about it because I'm still not over it.
Do you feel you're over it?