Wasn’t she basically Ari Onassis’ “Beard”.
I've read numerous Kennedy bios, and several Ari books. He wanted her as a "trophy" wife, because he craved the publicity. She wanted his money, and the privacy he could provide for her and her kids. At least on her terms, anyway. When she wanted publicity, she got it, when she wanted privacy, she stayed on Skorpios or the yacht, and Ari could guarantee that privacy.
I've never seen any indication that Ari or her fooled around when they were married. All indications that they cared for one another. Did they really love one another? Who knows? But she sure did like the money.
Ari just went to pieces when his son (Alexander) was killed in a plane crash in 1973. Heavy drinking, etc. He died in 1975. Jackie squeezed $25 million out of Christina as a settlement to the estate.