Why are you "shocked" he wants you to watch him do kink with new girl? You say he and C are more into BDSM than you are. Have you watched them do kink? Would he ask C to watch him do new girl if you don't want to? I mean, C is more into that scene, she seems like the one to ask.
I am not a voyeur or an exhibitionist so I don't get this "watching" thing at all.
If C struggles with jealousy, seems to me the main problem is getting her OK with hubby being intimate with others, period, not his random feeling of increasing hotness with new girl by having his wife (who isn't very kinky at all) watch them do stuff!
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
me: Mags, 59, living with:
miss pixi, 37