So, from what I understand, you are in a poly V relationship, with your boyfriend as the hinge and you and girlfriend as the arms of the V?
Have you had any discussion about hierarchical poly? i.e. primary and secondary partners? Some people don't believe in it and some do. Personally, I believe in it, if only in the sense that it can help everyone understand where they fit in, in a clear way.
It sounds as if you are not quite sure where you fit?
As for him being affectionate when you are alone, but not in front of his friends... does that also include not in front of his girlfriend?
Sometimes poly people have a tendency to reassure their 'primary' (or original, older, longstanding) partner more than their 'secondary' (or new) partner in social situations.
I know that, to be honest, if I was with my girlfriend and a girl I was seeing, I'd probably give a little more affection to my primary girlfriend, because she is my priority and I don't want her to feel insecure. I only get involved with people who aren't jealous of my girlfriend, so none of them are phased if I give her a quick kiss. But - I would never cuddle and rub it in their face, either.
I think the very best thing for you to do would be to have a proper talk with your boyfriend and see where he sees you fitting in. You have the right to your own expectations, needs and desires... so now, it's about compatibility.
GalaGirl pointed out something really good to me... she told me that I metaphorically asked my girlfriend to get me a drink... but didn't specify what kind of drink... so my girlfriend is flailing about, bringing me all kinds of drinks to make me happy... I'm getting more and more annoyed about her not giving me what I want... but I haven't told her exactly what i want in the first place.
As for thanksgiving... I've got to be completely honest. If it were me, I'd just invite her along, out of human kindness and respect to her. Especially if you talk to him about where you stand; because you might not find it such a struggle to have them both there. Then outline your feelings on PDA... if it hurts you that they touch and you two don't... ask them to be considerate... (I know how it feels: I've watched my girlfriend cuddle her husband at family events, whilst ignoring me, for fear of her family finding out... and it sucks).
So, be honest, and good luck!
Me: (30f) open poly
GF: (40f) My long-term, long-distance partner
Hubby (37m): GF's husband
Garcon (26m): GF's submissive/third partner
“Peace comes from within. Do not seek it without." ~ Buddha