Val the "relationship" appears to work for you and the OM, at present, on all levels; and it could be regarded as adult and civilised.
But it's neither.
Civilised adults respect other human beings and allow them to make informed choices. You and OM have decided that the wife is not to be allowed autonomy of choice.
You have referred to her expensive hobbies, the 1/2 million pension pot, the children etc. with scant regard. You have gleaned this intellegence from OM and mutual friends. You have overtly referred to her as class biased, snobbish, expensively high maintenence etc. It's snide and it's a clearly unbalanced view.
The mutual "friends" are clearly not friends of hers; and I wouldn't believe OM's account.
Hopefully, the wife is not as duplicitous as the pair of you; otherwise; by default, you could find yourself in sexual contact with the tennis coach, stable hand, the gardener; and half of the local rugby team. Sexual health can't be guaranteed.
I hope that your adult approach to this relationship also includes regular visits to a GUM clinic.
Unfortunately, the wife wasn't afforded the same opportunity to protect her own sexual health, when you embarked on the affair with her husband.
You're in a position where you are with a man that is still having sex with his wife but doesn't have the balls to leave an "unhappy/superficial" marriage; ostensibly because of monetary issues.
What a catch. A man with no balls, and you get sloppy seconds sex when he can lie/fit you in; oh, I forgot; you also have to be willing to fit him in as well; so that's alright then; that's very Bohemian, adult, Avante garde.... no actually; it's just shit.
Nothing happens in isolation; unless you're a hermit.
You have impinged on his family; and there have been consequences. Those consequences may have made the "little woman at home"; the way she is.
So he drops down dead tomorrow; and you Val have never existed.
You can't stand by the graveside or watch him role into the crematorium because you are his dirty secret; and it aint much to show for being the OW for ten odd years.
Good luck with that.