So, in summary, I'm a hot mess right now and I know I did none of the things I should have. Please help with damage control.
Q1: You had a fun date. Are you interested in another date with him? Or planning it already?
Q2: "I did none of the things I should have."
Actually it isn't at all clear to me what you did wrong, at least in an open r/s context.
Can you elaborate on what you did wrong here?
Advice on damage control... .nothing special here about an open r/s. Your H is a pwBPD. Standard BPD tools should do the job as well as it can be done.
1. Boundary enforcement to prevent raging / circular arguments.
2. Don't invalidate him. Don't JADE when he accuses you of stuff.
3. Validation of his fears.
Advice on open r/s: My experience is with long term polyamorous r/s... .in that context... .if your marriage is a hot mess right now, don't start anything new. When involved with a pwBPD, that circumstance is all too common! [It is your call how much drauma is in your marriage right now, not mine

I did say "IF".]
The reason is that it doesn't seem to me to be fair to pull somebody else into a r/s with the unresolved conflict and crazyness. In addition, you probably are better off without adding anybody crazy enough not to care about mixing it up with that level of chaos! The sane ones will run away screaming!

Not sure if this applies to swinging / casual sex / casual dating... .No personal experience there.