In Sonnet 31 by Sir Philip Sidney, what does the last line reveal about Astrophel's view on love?

Astrophel and Stella is a series of sonnets by Sir Philip Sidney, each of which expounds upon a different element or emotion of Astrophel’s unrequited love for Stella. In Sonnet 31, Astrophel is addressing the moon, wondering whether Eros, even in the heavens, “his sharp arrows tries.” And if there is love on the astral plane, Astrophel further wonders whether it is the same as on Earth, and asks several rhetorical questions of the moon, comparing his own situation to the hypothetical circumstances of love in the skies. “Is constant love deem’d there but want of wit? / Are beauties there as proud as here they be?” he asks. In his final question, he asks of the moon, “Do they call virtue there ungratefulness?” This indicates that in Astrophel’s own experience with Stella, he has been labeled ungrateful by his love for demonstrating virtue.

We can assume that Astrophel’s view on love is dejected and somewhat bitter—he is feeling hopeless in his situation with Stella; his endless love for her is being ridiculed. He believes Stella is being proud in her rejection of him, and that she is taking advantage of his doting without any concern for his own deeply invested feelings for her. And so he turns to the moon, seeking solace in a companion to whom he can assign, and with whom he can share, his own feelings. Thus by asking the moon about the nature of love among heavenly bodies, he is revealing the nature of his own relationship with Stella, and revealing as well his despondence as his virtue, his dedication, and his loyalty are regarded with derision and turned against him in his quest for Stella’s love.