YTA
I sympathize I really do. I’ve been in your situation, and I’ve had my partner in your situation. I know how it feels to give unending energy to people who are struggling. I also value Nolan’s right to privacy. He most likely feels deep shame about whatever big struggles he’s facing.
However, all of that does not excuse you and your friends excluding your future wife and gaslighting her. Instead of infantilizing her, using code names and hushing when she walks in the room- why not just not talk about it at all? I thought Nolan is extremely private? How does he benefit from everyone talking about him? Don’t you guys have anything more entertaining to do with your time together? Also, it does not excuse the effect all of this is having on HER mental health. She should not feel intruded on in her own home. She should not have to lose sleep over this. She should not have to make up scenarios. I think if you value both relationships, you need to sit down with Nolan and explain a few boundaries to :
I bet that your energy put into this situation has taken a lot from your relationship. A lot from your own well being. A lot of spare time you could be using to participate in healthy activities that bring you and your fiancée a feeling of closeness and happiness together. If that’s less a priority than you friend, then you should cut her loose because a marriage will fail.
You’re not a therapist, and even if you were it would be highly inappropriate to give this level of investment (aka waking up just to smoke outside, as you’ve said it warrants no emergency response, sounds more like a habit).
EDIT: you’re his POA and you’ve failed to mention this to your fiancée? Omfg!!!!!