I was just straight up about it and I wasn't all that nervous about it. But in my situation, I wasn't having that convo with a partner of 10 years. I was having it with a guy I wanted to date that later ended up as my husband. So he's known from the get go.
If I were coming out to him now I'd be in mixed feelings. Not nervous to just stragight up it because -- shoot! It's my partner for nearly 20 yrs, right? We've had other big talks before, no prob.
On the flip side... shoot! It's my partner for nearly 20 years. I wouldn't be happy to find that poly was a deal breaker for him. The big talk would not be a prob but the result could be.
But I'd just spit it out anyway. Being honest is easier in the long run.