Quoting GiggleBellies:" My husband has gone lost his mind. He has been accusing me for the past 6 months of cheating on him. ... [snip!] ... course, he BLAMES ME. He has gone lost his mind!!! I think this is a boderline personality male. Anyone ever go through this?"
I'm not hearing anything about him being "normal" at times so that doesn't sound like BPD to me. Is he abusing any legal/illegal substances or alcohol?
Also, I wouldn't leave unless he wasn't willing to admit there was a problem or seek therapy. It sounds like there may have been a traumatic experience from his past that is creeping back and he's allowing those thoughts to control your relationship. Therapy may help if he's willing to try it. Good luck.