Let me ask you a few questions if I may...
Do you have the impulse to kiss or be affectionate, but you suppress it? Or do you just not have the impulse at all?
Do you feel like if you become affectionate it will be viewed by the others in your relationship as clingy? Do you think it will degenerate into a tit-for-tat?
Do you think that you'll be hurting the feelings of the other bf if you're affectionate? Or angry?
Are you worried about what the community will think?
Lastly, do you see yourself as an equal (if that's the relationship you've all agreed upon) to the other bf and just as deserving of affection from your shared partner?