Poems about the seduction of a chaste mistress were a staple of the English Renaissance. For example, "The Flea" would make an interesting comparison to Andrew Marvell's famous "To His Coy Mistress" (paper topic!). Both poems urge the ladies in question to quit fussing around and get down to the business of lovin'. Rather than trying to arouse his beloved, the speaker appeals to her sense of reason. Maybe he believes that she is already itching with as much desire as he is; she just needs help getting over those last scruples.
The poem is narrowly focused on the speaker's sexual desire and does not take into account any preexisting relationship he might have with the woman.
"Marriage" in the poem is merely a euphemism for sex.