AHEM.
https://en.wikipedia.org/wiki/Impostor_syndrome
Your rules do not apply here.
This is a very real thing that happens to real people and has real consequences in real life. And it says "Fuck you sideways with a cactus" to any type of logic that states "But you have no reason to feel that way!"
Anxiety and depression are real diseases, and like any disease, they will not be satisfied until your are dead - either through suicide or by health complications. That is not hyperbole, that is an absolute.
https://pmc.ncbi.nlm.nih.gov/articles/PMC5082973/
https://pmc.ncbi.nlm.nih.gov/articles/PMC5113020/
https://www.healthline.com/health/can-depression-kill-you
https://www.verywellmind.com/can-depression-kill-you-1067514
And for those who suffer from these diseases chronically? There are no magic bullets for this. You are never "cured". It is something you can easily relapse into. It is something that is baked into the actual neurons in your brain, and there is fuck-all anyone can do about that.
It lurks in your head. It whispers in your ear. It makes those suggestions that make you second-guess yourself constantly. It tells you that you're a fraud and a charlatan. It always tries to bring you down when you're at your highest. It never goes away. Instead, it just waits for the right moment to strike.
It is a living hell. It is a constant battle. And it will exhaust you, no matter how much mental fortitude you have. Because even if it can't get through your mighty walls, it'll just dig out their foundations instead.
The author/mangaka has decided to write about this thing, and they are doing fucking fantastic job of deconstructing the typical fantasy and polycule-romance tropes - where even if it's a dream come true, where two beautiful, powerful, but flawed girls from the most powerful families in the world both love you and adore you for who you are and they both want to work together to make sure you are loved, you are still going to feel that you're not worthy of them because anxiety is a fucking monster that way.
Trust me. I'm taking some
very strong antidepressants, and sometimes all it can do is just take the edge off. If someone wants to be
my wife? They absolutely
must be 100% committed to pulling me back to safety when I'm at my worse, and they must be prepared to do so at a moment's notice.