I've a good friend with Bipolar. 99% of the time they are as rational and competent as anyone I know. But there are times when they get manic. During that phase everything is amazing they are amazing and every decision they make is brilliant.
Only you know that in a couple of weeks that the depression is going to hit and if you don't help will have done things that they regret. Things that lead them to getting fired, spending too much money etc. And you're going to feel super guilty trying to comfort that person if you didn't do everything you could to stop them.
If in that manic phase they decide you're only gas lighting them, they wont listen. You just have to sit back and hope it doesn't get too bad. Hope that they don't wipe out everything they spent the last 5 years investing in.
I don't really care what label you use. But there are professionals that can help. Even in a non manic state my friend wont go beyond the GP. They've been on the same medication for decades. There must be more that can be done. More than just going back for a repeat prescription from a GP that has never been told how bad it gets.