Benwick/Louisa was just a cover story. He was really talking about himself and Anne.

Absolutely so, and JA gives us an extra little clue to this that I only noticed on this reread (amazing how there's always more to notice):

Here's FW on Benwick's attachment to Fanny Harville: "A man like him, in his situation! With a heart pierced, wounded, almost broken! Fanny Harville was a very superior creature, and his attachment to her was indeed attachment." (ch. 20)

And here's FW on his own feelings about Anne: "You pierce my soul. . . . a heart even more your own than when you almost broke it. . . . Too good, too excellent creature!. . . . You do believe that there is true attachment and constancy among men." (ch. 23)