Bright star! would I were steadfast as thou art—
Not in lone splendour hung aloft the night,
And watching, with eternal lids apart,
Like Nature's patient, sleepless Eremite,
The moving waters at their priestlike task
Of pure ablution round earth's human shores,
Or gazing on the new soft fallen mask
Of snow upon the mountains and the moors—
No—yet still steadfast, still unchangeable,
Pillow'd upon my fair love's ripening breast,
To feel for ever its soft fall and swell,
Awake for ever in a sweet unrest,
Still, still to hear her tender-taken breath,
And so live ever—or else swoon to death.
As he rests on her breasts he feels her breathing; the movement, the ‘soft fall and swell’, is highly erotic.  Note also the soothing, whispering effect of the  alliterative  ’s’s in this line.