Hello and welcome! I personally don't mind reading long posts if they are as well articulated and thought of as yours is.
Do you have a specific thing you'd like to ask? From a quick read, it seems you are just rewording how you feel. I don't mean to belittle anything when I use "just" -it's a huge accomplishment to become so self-aware as you are now.
Couple of questions:
1) Have you talked with your metamour, or is all of your knowledge of the situation second-hand?
2) Do you have or imagine having any other relationships? How about your bf? How about your metamour?
3) How would you feel if they called off the divorce and staid married? How would you feel if they resumed an occasionally-sexual relationship, instead of just keeping it as a possibility?
You've probably read a ton of similar stuff, but I just want to quote this months issue of DIVA, which ran an article on asexuality:
"However, just when we thought we had asexuality down, Kayleigh throws us a curveball by telling us she enjoys kissing, has the ability to fall in love and has sex with her girlfriends occasionally. This begs the question, if person partakes in what most people perceive as sexual acts, can they really be asexual? Kayleigh explains that her reason for occasionally having sex with her girlfriends is because she knows it pleases them. However, she clarifies that it's never something she is coerced into doing. 'I don't think it's fair that I get most of what I need from the relationship and they don't, to which they said they'd rather not have sex than make me uncomfortable,' she tells me.
She also enjoys kissing, but unlike most of us, never sees it as a prelude to sex: 'Kissing feels good, like hugging or holding hands. I could spend an hour just kissing someone in bed, naked, and it would never cross my mind that it would lead to sex.'" (DIVA magazine May 2012, p. 55)
Me: bi female in my twenties