I know in group conversations that light and dark side points are decided not by the winner of the conversation roll but the choice that you selected. How about with companion affection? I pretty much know which conversation option will cause a gain in affection points with my companion, if I select the option and my groupmate wins the roll will I still gain the affection points I normally would have if I were doing the conversation on my own?
If you do not win the conversation roll, then since you didn't say it, the companion does not get any affection points.
You have to both choose the appropriate option to gain (or lose) affection with the current companion, and win the roll.
Of course your companion must be summoned and in the group, so this only works for groups less than 4.
It is not like Light/Dark side choices where you get the points for what you chose regardless of who won the roll.
Same way as LS/DS points work, you get/lose affection based on what you choose, though in specified group content (Heroic/Flashpoint stuff) there don't seem to be any conversation triggers tied to companions to cause it.