In this excerpt from “porphyria’s lover” by robert browning, which lines suggest that the speaker doubts the depth of porphyria's love?

and spread, o'er all, her yellow hair,
murmuring how she loved me—she
too weak, for all her heart's endeavour,
to set its struggling passion free
from pride, and vainer ties dissever,
and give herself to me for ever.
but passion sometimes would prevail,
nor could to-night's gay feast restrain
a sudden thought of one so pale
for love of her, and all in vain:
so, she was come through wind and rain.