This poem is a passionate expression of sexual love. The speaker admires the beauty of Amarantha (specifically her hair) after they have had sex.
In the first stanza of the poem, the speaker addresses a woman, named Amarantha, and tells her not to braid her hair, to let it "fly" loose. In the third line of the stanza, he compares her loose hair to his "curious hand," the implication being that his hands are free to explore her hair, or maybe even her body.
In the second stanza, the speaker says that Amarantha should let her hair be as "unconfined" as the wind. In the last two lines of the stanza he says that the wind has left its darling, "th' East" (perhaps meaning the sun) to come and play with Amarantha's hair, which he describes positively as "that spicy nest."
In the third stanza, the speaker compares Amarantha's hair to "golden thread," suggesting that it emits a golden light because it is so radiant. Otherwise, he simply repeats his instruction for her to let her hair hang loose, or be "neatly tangled at best."
In the fourth stanza, the speaker says that Amarantha should not tie up her hair ("that light") and that to do so would be like ruining a clear night sky with clouds. He tells her not to "o'er-cloud" the night. In the last two lines of the stanza, he suggests that she has sunshine in her hair, and that when she shakes her head, the sunlight "scatter[s]" outwards.
In the fifth stanza, the speaker says, playfully, "See 'tis broke!" He means that Amarantha has shaken her head and that is why day has now arrived. The implication is that the speaker and Amarantha have spent the night in "this grove," under the trees ("The bower"), and now the sun has risen. The speaker and Amarantha are "Weary" and "panting," implying that they have been having sex.
In the sixth and penultimate stanza, the speaker suggests that they should "cool our fire," meaning their sexual passions, in a bath of milk or cream. The milk and cream are probably euphemisms for the bodily fluids released during sexual intercourse. The speaker says that they should bathe in "cream below" and "milk-baths" until "all wells are drawn dry." This is another sexual euphemism. The speaker is suggesting that they keep having sex until they can't have sex anymore, or, in his words, until "all wells are drawn dry." In the last line he says that when this happens, he will "drink a tear" from her eye. This implies that the speaker is desperate for every last drop of passion from his Amarantha.
In the first two lines of the final stanza, the speaker reflects that the "joys" he experiences with Amarantha momentarily distract him, and her, from any "sorrows" that they might otherwise feel. They can "deceive" their sorrows, or forget about them momentarily, by being with one another. In the final two lines of the final stanza, the speaker reflects that they might also "weep" that they can "so little keep" these moments together, meaning that it's sad that their moments together are so brief and can't last forever.