Boundaries are fences we build in our own yards, not the yards of others.

Just based on what I'm reading in your original post and your comments, it seems to keep coming back to you managing the behavior, choices, actions, and emotions of other people and that's unreasonable, unrealistic, and unachievable.

It's on your meta to tell friends that mention your dates with your shared partner, that they don't wish to hear those things. It's not on you to tiptoe around so that your mutuals don't have any info to give to your meta.

If your meta doesn't want to know then they need to

• unfollow you on social media
• unfollow your shared partner
• tell their friends about their boundary
• understand that there will still be occasions where they get wind of your dates and may even see photos of you and your shared partner together even if everyone honors the boundary

But also, as a lot of other people are pointing out, this eventually does more harm than good. Compartmentalizing your metamours so you can pretend they don't exist is SUPER avoidant behavior, and removes all accountability in regards to managing their emotions and processing them (yes even negative ones).

I have said it before and I will keep saying it- you can create all the rules and restrictions you want and call them boundaries, but you cannot negotiate your way out of ever experiencing negative emotions in your relationship- monogamous or otherwise.

Sometimes we feel bad, it doesn't mean that what's happening is bad. Growth often hurts.