To me the end is quite clear ***Spoilers***
Having gotten off my disappointment, I also want to contribute my 2 cents to the strange things towards the end.
To me, Marswell is by all means set on the character played by Grace. He tries to get this through to her anthropologist, over and over, and everyone else also knows ... but always, Don, the husband, is so convincing when speaking about his love to his wife, he is so full of praise of her, that Marswell kind of has second thoughts of breaking up this marriage. So he gets drunk and plays fervently with Kelly (not the one with grace), and when Grace comes, he pretends to find nothing in her, and even says so. Quite contrary to his feelings. Kind of Casablanca-style 'I do the thinking for both of us'.