It took a long time in my life to make the distinction between honesty and privacy. (long before poly came my way, I learned this)
My men were best friends before I knew CurrentBF very well. CurrentBF cannot be told anything that you don't want anyone else to know. anything. If you want a secret kept, FirstBF is an excellent choice, for one, because he'll forget, and for two, he doesn't talk to many folks.
Between them, it's been an interesting road for me to walk. CurrentBF doesn't really have a jealous bone in his body, though he has a few (very few) insecure sinews.
He wouldn't mind anything I wanted to tell him. FirstBF, as mentioned, is extremely private, and I know he would be uncomfortable if I told CBF many details about us. I also know FBF doesn't especially want to hear about me and CBF.
So, while what I did in bed with FBF this weekend is not a secret, it is private and no one's business but mine and his.
I did wake up from dreaming that CBF had come to visit us in bed, and I was in the middle, and we just having the friendliest, social visit with each other (all naked). No one seemed to notice that we were all in bed together naked, we were so caught up in our chatting. I mentioned something about how I could die now because I was the happiest girl in the world. Then FBF got uncomfortable and CBF left, and FBF was miffed with me because CBF left. <- weirdest dream in a LONG time. But I was able to tell FBF the short version of it when I woke up; and I can hardly wait to share it with CBF.
I don't know if that's at all helpful, but some things I think about when I think about sharing intra-relationship stuff.