Jerrold E. Hogle appears to be answering the question--"why not true to me?" (171)--with the following statement:
To approach this newly unified, objectified, and uplifted absolute, the speaker must rush into a quest from one "shadow"-woman to another [...], all of whom seem to harbor a few of the standard's qualities (making each attractive) yet each of whom soon reveals a lack or perversion of the rest, driving the seeker away and onward. Indeed, the dream-ideal's myriad ingredients, forms, and potentials force the lover, so that he can come closer to encompassing their multiplicity, to increase the number and variety of "secrets" he tries far beyond the smaller number in the lover's autobiographies of Dante and Petrarch. That bewildering succession, moreover, starts to establish how radically separate the standard really is from goddess-hood and simple objectivity. "Wounded," like Prometheus as Acteon, by the disappointment that must result from any quest for a supreme form by way of inadequate substitutes, the speaker stands "at bay" by "turn[ing] upon [his] own thoughts" (ll. 273-74), by confronting the fact of the basic and projective psychic process that looked to an other of itself to complete itself in the first place. (281)
Hogle, Jerrold E. Shelley's Process. New York: Oxford UP, 1988.