Just to add something from the "other side" -
MrS originally had a boundary/rule that requested that he would be "informed" if sex between Dude and I was going to happen (a "soft-limit" in GalaGirl's terminology). His perspective was that he wanted to be able to "brace himself" if he was likely to come upon situation where we were having sex (because we all live together) or, at least, know why I wasn't responding to his texts/calls.
I, to be honest, was fine with this limit - I was asking my husband to adjust to a whole new dynamic (sex with Dude vs. sex with girls). Dude was not as content with this - he felt that it restricted spontaneity.
Six months later - it was a moot point (and has been for the last 18 mos). The restriction/boundary/rule was lifted. MrS is no longer uncomfortable with Dude+I sex wherever/whenever - whether he is there or not, whether he could walk in on us or not. Sometimes people require things during a transition in order to find out whether they can weather the transition.
So - yes, find out if it is a hard/soft limit. Find out, if possible, what the restriction is meant to accomplish. Yes, it is a red flag - BUT a red flag means "Stop! assess the situation." If, after assessing the situation, you decide it is only a "Yellow Flag" (Proceed with Caution)...then you should ...well, "proceed with caution".
Me: poly bi female, in an "open-but-not-looking" Vee-plus with -
MrS: hetero polyflexible male, live-in husband (22+ yrs)
Dude: hetero poly male, live-in boyfriend (3+ yrs) and MrS's best friend
Lotus: poly bi married female, "it's complicated" relationships with Dude/JaneQ/MrS (1+ years)
+ "others" = FBs, FWBs, lover-friends, platonic G/BFs, boytoys, etc.
My poly blogs here:
The Journey of JaneQSmythe
The Notebook of JaneQSmythe