So, a status update if you'd like to read it.
Honestly, when posting the OP my main goal was to vent. I didn't expect anyone to give me a practical solution to my problem. Sometimes, though, strangers surprise you by understanding you very well. Other times they get what you say so completely off mark, that it makes you think and re-evaluate your perspective. In this case it was the latter.
In fact, it was this comment by Marcus:
Originally Posted by Marcus
Even as just a booty call I couldn't imagine wanting to be in that for long.
When I first read that, I literally laughed until it hurt. 'This guy thinks this is about the sex
?!', I thought to myself, 'A and I haven't had that for like 10 months, even before she started her relationship with N!'.
But, that got me thinking. And after a lot of thought, talking with A, changing my perspective and talking again, we've reached a possible solution that I'm much happier with: She gets to be monogamous with N, and we get to stay friends.
This is most of what she wanted, and is practically the same situation we have now, but somehow changing the words around and defining it like that makes me feel much less like I'm involved with deceiving someone else, or in a relationship structure I find unethical. What a difference words can make
So in a weird way, thanks Marcus for your perspective
And thanks everybody else for your thoughts and advice. This has been a positive surprise.