Srimad-Bhagavatam
SB Canto 6
Illicit sex is strictly prohibited. One should be satisfied with his married wife, for even a slight deviation will create havoc. A Kṛṣṇa conscious gṛhastha should always remember this. He should always be satisfied with one wife and be peaceful simply by chanting the Hare Kṛṣṇa mantra. Otherwise at any moment he may fall down from his good position, as exemplified in the case of Ajāmila.
SB 6.1.64, Translation and Purport: Thus Ajāmila began spending whatever money he had inherited from his father to satisfy the prostitute with various material presentations so that she would remain pleased with him. He gave up all his brahminical activities to satisfy the prostitute. There are many instances throughout the world in which even a purified person, being attracted by a prostitute, spends all the money he has inherited. Prostitute hunting is so abominable that the desire for sex with a prostitute can ruin one's character, destroy one's exalted position and plunder all one's money. Therefore illicit sex is strictly prohibited.
One should be satisfied with his married wife, for even a slight deviation will create havoc. A Kṛṣṇa conscious gṛhastha should always remember this. He should always be satisfied with one wife and be peaceful simply by chanting the Hare Kṛṣṇa mantra. Otherwise at any moment he may fall down from his good position, as exemplified in the case of Ajāmila.

Comments
BG Chapters 1 - 6
Lusty intelligence influences the
spirit soul to acquire the false ego
and identify itself with matter, and
thus with the mind and senses.
BG 3.40, Purport: The enemy has
captured different strategic
positions in the body of the
conditioned soul, and therefore
Lord Kṛṣṇa is giving hints of those
places, so that one who wants to
conquer the enemy may know
where he can be found. Mind is the
center of all the activities of the
senses, and thus when we hear
about sense objects the mind
generally becomes a reservoir of all
ideas of sense gratification; and, as
a result, the mind and the senses
become the repositories of lust.
Next, the intelligence department
becomes the capital of such lustful
propensities. Intelligence is the
immediate next—door neighbor of
the spirit soul. Lusty intelligence
influences the spirit soul to acquire
the false ego and identify itself
with matter, and thus with the mind
and senses. The spirit soul
becomes addicted to enjoying the
material senses and mistakes this
as true happiness. This false
identification of the spirit soul is
very nicely explained in the Śrīmad-
Bhāgavatam (10.84.13):
yasyātma-buddhiḥ kuṇape tri-
dhātuke
sva-dhīḥ kalatrādiṣu bhauma ijya-
dhīḥ
yat-tīrtha-buddhiḥ salile na
karhicij
janeṣv abhijñeṣu sa eva go-
kharaḥ
"A human being who identifies this
body made of three elements with
his self, who considers the by-
products of the body to be his
kinsmen, who considers the land of
birth worshipable, and who goes to
the place of pilgrimage simply to
take a bath rather than meet men
of transcendental knowledge there,
is to be considered like an ass or a
cow."