What they said.
Your relationship with your BF is just that - YOUR relationship. If you also want public validation of your relationship, talk about it. Tell them that this rule is not working for you, and renegotiate. Maybe an interim solution (until you're all comfortable with it) is to NOT all hang out together unless nobody displays affection. Why put yourself in a position that makes you upset or uncomfortable?
Mono. Divorced, two kids (DanceGirl, 14; and PokéGirl, 11), two cats, one house, many projects.
My partner. Poly. In relationships with me, Xena, and Noa.
Poly. In relationships with Chops and Noa, and dating others.
Married, Poly. In relationships with Chops and Xena (individually).
Blog thread: A Mono's Journey Into Poly-Land (or, "Aw hell, there's no road map?!")
Slightly more polished blog with a mono/poly focus: From Baltic to Boardwalk