(The following from Franz Hartman, quoted by Percival on page 91.)
"Woman as such represents the will (including love and desire), and man as such represents intellect (including the imagination). Woman represents substance; man represents spirit. Man imagines; woman executes. Man creates images; woman renders them substantial.
The divine man (the angel) is male and female in one; such Adam was before the woman became separated from him."
(Blake disagreed emphatically with the biblical creation story, Blake considered the separation of the original Adam into male and female as more of a Fall than a Creation. Of course you and I and Blake as well are faced with the Reality of our circumstances.) At any rate after the Fall:
"Man was like the Sun; woman as such resembles the Moon, receiving her light from the Sun, and man without woman (in him) is a consuming fire in want of fuel."
This means that Blake (and Paracelsus) in their use of sex have a primarily metaphysical rather than a physical connotation. Nevertheless Blake began working with a sexual hangup of some sort, which he seems to have satisfactorily worked through with some 40 years of happy marriage.
In the Christian faith marriage is a sacrament, and for many of us the primary sacrament. However living the sacrament was no more common in Blake's day than in ours. 18th and 19th century England seemed largely to view marriage more as a commercial transaction.