My girlfriend would be a much better person to answer this..and probably will! I am her secondary and essentially she is the focal point of a "V" between me and her husband. I don't have the issue you have as I only have intimate love for her. She is more closely in your position as we are often all together and ocasionally there is another friend of hers and his as well.
I do my best to respect all of us and although the affection is there I interact more like a close friend in those situations. I have zero issue with jealousy towards her husband and although I am completely comfortable with them showing affection towards each other I do not expect open affection to be displayed to me. We have our own and very private times for that. In fact I probably shy away from displays in a teasing and humorous way. My favourite expression is "you are going to get me in trouble"!
I believe she has read your reply and will post a response herself. She has an infinite capacity for love and doesn't get my inability to intimately love more than one person either. Oh the sweet challenges we face..but we do it together..all three of us!
Thanks for the discussion.