"'if life did not make duties for us before love comes—love would be a sign that two people ought to belong to each other. But. . . . I must not, cannot seek my own happiness by sacrificing others. Love is natural—but surely pity and faithfulness and memory are natural too.'"
George Eliot, The mill on the Floss III.vi.11, "In the lane" (ed.
with an introduction and notes by A. S. Byatt (London: Penguin Books, 2003
One question would be whether this is really duty speaking, or only one of the voices within Maggie. Cf. the narrator at IV.vii.2, "St Ogg's passes judgment" (517 ff.), which comes after Maggie's important response to Stephen in III.vi.14, "Waking" (495 ff.), but not after she has come out on the other side of "The last conflict" (III.vii.5) and been fixed in that position by her final act of self-sacrifice.
If it is, as I believe, duty speaking, then the narrator at IV.vii.2 (517 ff.) is speaking for Stephen in III.vi.14 (495 ff.), not Stephen for the narrator.