Hi WhichWayUp,
welcome to this website. it's an important first step (and a brave one) to make your very first post. I would recommend you come back often. Both to read and to post.
a couple of thoughts on your question.
Should I share with him what I know about bpd? Will that help him get treatment? Or is that just a bad, bad idea?.
the general recommendation is to be very cautious about sharing this type of information. Let me explain why.
first - it is very hard to diagnosis BPD. many times BPD is comorbid with other disorders (meaning existing together) and BPD can be experienced in ways that are very similar to other disorders CPTSD comes to mind.
second - depending where you are located BPD comes with a stigma attached. the mental health system is a hodge podge of resources and in some locations treatments centers and therapists are reluctant to take on BPD sufferers because of the amount of effort/energy they require. thankfully this happens less now than it did,... oh lets say 10 year ago but it is still a concern.
third - as Diddle mentioned,.. some times the focus on mental health or BPD causes your own personal situation to get worse. BPD is a disorder that has a lot of shame and instable self image attached to it. Telling some one that you think they might have BPD can make shame and instability rocket out of control.
so how is it recommended that the topic is addressed? start small. pick one symptom or issue that is troublesome to your husband. talk about that ... use I statements. "I've noticed that you seem frustrated and stressed much of the time do you think that...". "I'm finding the rage and anger to much to cope with, we need help to make this work..."
avoid labeling. "I've researched it and I am sure you have BPD" creates a ME against THEM dynamic. You on the side of the mental health professionals against him... most people who have the traits of BPD feel like victims. You want to avoid encouraging that.
Plan the conversation carefully. think about what you want to say and how he will receive it. most people don't take well to 'hey I think you have a mental illness'.
and consider therapy to support you... this is a tough road.
hope this helps
'ducks