I found a really good quote in
Lamps of Western Mysticism.
"...I am haunted with a feeling that it was used once by St. Thomas. Most of us have known its experience in the human order. The fall is from the sufficiency of self in its own centre. The love of any object in humanity decentralises the true lover. It transfers preoccupation from the self within us to the self without of another. It is an absorption in contemplation of the visible beauty. But mystic love implies the secret of contemplative absorption in an absent beauty, and it is the realisation of this beauty in the heart of mind. ...
This suggests to me that Waite does see Eden as a place where the lovers were united by their mutual love of the divine, and the winged figure is indicative of that love. It is a love which focuses on the divine, but in doing so, partners them as well. Physically, they're not together, but that's right because if they were, they'd be in love with each other, and that would mean that they'd lost their way, lost that higher connection.
If so, then for Waite, a true love, and a true marriage, has to be one brought together by a mutual love of the divine and dedication to a higher power.
The fall, it would seem, for Waite is giving into love for another and losing sight of the divine. The temptation to give into that is there with the snake behind Eve. Once it happens, men have to take a more difficult path to get back to that Eden. The path of the tarot, which goes between the pillars. The path between the Tree of knowledge and that of Life.
Maybe?