How would Spenser's treatment of human sexuality in Amoretti compare to that in Epithalamion?
There are many significant differences between Spenser's Amoretti sonnets and his celebratory wedding Epithalamion. Aside from the style and structure of the two, the Amoretti chronicled the passage of real events in real time, i.e., Spenser's courtship of Elizabeth, while the Epithalamion celebrates the real event of their wedding day and night.
Since the two tell of two vastly different [then] experiences, that of courtship and marriage, the topic of sexuality is foreign to one and natural to the other. As a consequence, the treatment of sexuality in Amoretti is veiled and subtle while in Epithalamion it is gently overt.
An example from the Amoretti sonnets is in Sonnet 5 in which, in veiled terms, Spenser speaks of looking at Elizabeth with lust as indicated by Threatening rash eyes:
Threatening rash eyes which gaze on her so wide,
That loosely they ne dare to look upon her.
An example from Epithalamion is in the 18th stanza (also called 18th poem). The wedding is ended, and Spenser and his bride have the night ahead of them. Though there could be no occasion to speak of marital intimacy in his courtship sonnets, Spenser is now free to speak of it and does so in a metaphor of what awaits them under the cover of night sable mantle:
[Night] Spread thy broad wing ouer my loue and me,
that no man may vs see,
And in thy sable mantle vs enwrap, ....
[Night] Spread thy broad wing over my love and me,
that no man may us see,
And in thy sable mantle us enwrap, ....