I know in a lot of bipolar mania, there will be OPs. I read on one site there is a 90% divorce rate for bipolar sufferers, and there was never a standing forum, but several 'divorce recovery' forums I found on those sites.
Could be in this case either the author didn't know about any OW, or he could have been one of them that didn't go that route. I think if my H truly is bipolar, that his mania prior was expressed with illogical spending to alleviate pain, and alcohol use. I don't really suspect any other OW.
But having said that...I agree with Anjae, that this is another MLC case. It would be so incredibly rare, if not impossible, for a mood disorder to hit that late in life so randomly. I do think we'll find MLC is somewhere on this spectrum someday, but I am fairly secure that it's a separate thing.
But also - I don't tell people that. After I found this site I would sometimes tell people, "It's MLC!" and they would giggle, and say, "No, that's not what that is," due to the preconceived definition MLC carries with it. But if I say, "bipolar," the same people want to pray for us both. I go with that one publicly.