Hi DigitDoug!

I can definitely relate to what you're going through. My husband is, I strongly believe, an undiagnosed person with BPD. When he's in one of his moods, I'm his primary target. He will remember every negative thing I ever did and bring it up to beat the dead horse some more. Or he'll bring up something I never even knew was a problem. He'll preface it with "I'm not criticizing you, but... ." Last night, it was my dusting skills. First time he's mentioned that at all.
And the "I obviously married the wrong person" thing? My husband has said that many times too. Sometimes in the same conversation as "I love you more than anything in the world. I can't lose you." It's enough to make your head spin right off your body. It's part of the BPD and it's not rational. But, in a BPD way, it makes sense. I've believe that in my case, it's him pushing me away ("I have to push people away before they abandon me") and then also desperately hanging on. The two sides of the Fear of Abandonment coin.
For them, their feelings are facts. If you somehow make them feel bad (even unintentionally) or you don't validate what they're feeling or feel what they're feeling, then you become "bad" or the enemy somehow. When he gets worked up about something and I don't, it tends to trigger him because he feels like I should feel exactly the same way. They can't handle what's going on inside so they project onto us. It is very hard to be the barrel they dump all this into.
Sometimes what H lashes out at me for, I know, is actually something he sees in himself.
Walking away is, sometimes, the best thing you can do. You're fortunate you're able to do it. I tried it a few nights ago and wasn't physically able to since H followed me and just kept going.
I just joined this board a little over a month ago but I've already found the advice, input and support of fellow board members invaluable.
Very best wishes to you!