The love in marriage is from its origin and correspondence heavenly,
spiritual, holy, pure and clean above every other love which the
angels of heaven or men of the Church have from the Lord. It is such
from its origin, which is the marriage of good and truth; also from
its correspondence with the marriage of the Lord and the Church. If it
be received from its Author, Who is the Lord, sanctity from Him
follows, which continually cleanses and purifies it. Then, if there be
in man's will a longing for it and an effort toward it, this love
becomes continually cleaner and purer. All who are in such love shun
extra-conjugial loves (which are conjunctions with others than their
own conjugial partner) as they would shun the loss of the soul and the
lakes of hell; and in the measure that married partners shun such
conjunctions, even in respect of libidinous desires of the will and
any intentions from them, so far love truly conjugial is purified with
them, and becomes successively spiritual.
--_Conjugial Love, nn._ 64, 71