When my wife and I expanded into poly, we had a rule that was more or less don't-ask-don't-tell. This isn't a thing where I was uninterested but... well, I have a very "unique" network of friends and my dating pool is somewhat limited to that network. My wife is also part of that network and in the beginning, I was afraid that our relationships inside it would affect our relations to the network for the purpose it exists.
So for a while, I knew she was seeing someone else and having sex, and the curiosity grew and grew and I could feel that she was feeling stiffled by not being able to share a very big part of her life.
So, it was a bit difficult to talk about it at first, but we shared and agreed to rescind that rule. The next day, I met someone she was just getting into. He was an older professional man who reminded me a lot of the CEO of the company I work for. It felt so awkard because It was like "So... You're gonna be screwing my wife. Cool. And man, this snow, it sucks, huh?"
I didn't know how to relate to him. There's all kinds of dynamics, and there doesn't seem to be any kind of open-etiquette. :P
It wasn't all that exciting, to be honest. But it was interesting to see how my wife and I reacted, and later to compare notes and chuckle at the awkwardness of something new.
I'm sure it'll get more comfortable and natural as it happens more, and as my wife meets my signifigant people as signifigants.