(Oh crap. Just wrote a whole big post and got auto logged out and now have to run out to p/u run-out-of meds. So, I'll attempt the gist of it...)

I relate very much to a lot of the behavior you wrote about. But my BF is not bipolar. Does he have Borderline Personality Disorder traits? You better believe it. (Btw, psych's opinion too, not just mine).

Really glad to hear you are working with boundary and codependency issues! Uber-necessary when you can say:
"My compassion can get confused a bit to the point I might enable..."
Again, I relate.
"I'm a nice person and have learned to set boundaries....except when things become murky and that is where I am."
Me too.
There's quite a bit in your post that shows some successfully planted self-doubt, like:
"...maybe he's right, maybe I am mean, unreasonable, a nag, belittling, hurtful, etc. Perhaps he was right that I could have not said something or did something a certain way to set him off."
Essentially suggesting you should walk on eggshells and feel responsible for his behavior. No.
(Have you ever read Stop Walking on Eggshells? It's a good one.)
Good to be aware that that's what it is, so that you can maintain your resolve.

(I have to run now, but quickly -- I understand your coming with questions, I've had the same inclination in trying to understand Borderline, because for the life of me, I can't understand it (understand intellectually, yes, relatibility, no), and don't think it means everyone is the same, and I didn't read that in your post either. )