Why would I want to change? I know I'm being potentially belligerent here, but isn't this forum about accepting one's self as they are?
No, not belligerent at all, man! You make an excellent point. If you're comfortable in your own skin and confident that you are the way you want to be then stay with it!
I wrote "assuming you might want to change" because quite a few people who come to the forum do
want to change the way they deal with relationships.
I've no urge to preach poly or mono to anybody, and I think most people on the forum accept that both lifestyles and all the shades between are intrinsically OK. No problem.
You write, though, that both you and your wife's BF are monogamous. This is a little hard for me to get my head around: to me, in my purely subjective interpretation, it means that both you and he would prefer to be the only man in her life.
Yet you seem to respect the man and you appear OK with some aspects of their relationship. I admire your psychological flexibility!
With respect to finding a balancing partner for the relationship you write, "...finding someone who understands and is also available and etc etc, is 1 in a million." Well, maybe those odds are a little too long...but I feel your pain. I need more female companionship than I get from my poly GF but the hiking buddy I've found doesn't really understand poly, let alone accept it. I can feel her distancing herself lately, and I would guess that she's struggling with keeping it platonic while also realizing that I'm not going to give up my GF and fall with relief into her monogamous arms.
And this was just meant to be a hiking friendship!
So it goes.