Without experience with someone who's diagnosed its honestly a hard concept to grasp. I would just try to explain it for what it is, bipolar is when the chemicals in your brain are unbalanced which can cause a list of symptoms such as strange thinking, depression, disassociation, mania, etc.

Them wanting to understand and doing their own individual research is important. Not a significant other, but my grandmother did that very thing when I went through my diagnosis. Even then, when new things they don’t understand come up, rather than becoming upset that they don’t know, explain to them what you are feeling and experiencing and how/if they can help when it happens. Communication communication.

Its so hard for someone who doesn't understand our disease to understand what we go through. When I was married what helped was having him go to therapy with me once a month, having him research BiPolar and open communication