What kind of sex life can one lead, living in the material world?

Question: 
What kind of sex life can one lead, living in the material world?

(An excerpt from the book Perfect Questions, Perfect Answers—a conversation between Brahmatirtha dasa and Srila Prabhupada)

Srila Prabhupada: The Vedic principle is that one should avoid sex life altogether. The whole Vedic principle is to get liberation from material bondage. There are different attachments for material enjoyment, of which sex life is the topmost enjoyment. The Bhagavatam says that this material world...

pumsah striya mithuni-bhavam etam
[ Srimad-Bhagavatam, 5.5.8]

Man is attached to woman, and woman is attached to man. Not only in human society—in animal society also. That attachment is the basic principle of material life.

So, a woman is hankering or seeking after the association of a man, and a man is hankering or seeking for the association of a woman. All the fiction novels, dramas, cinema and even ordinary advertisements that you see simply depict the attachment between man and woman. Even in the tailor's shop you will find in the window some woman and some man.

pravrittir esha bhutanam
nivrittis tu mahaphalam

(Manu Smriti, 5.56)

So this attachment is already there.

Bob: Attachment between man and woman?

Srila Prabhupada: Man and woman. So if you want to get liberation from this material world, then that attachment should be reduced to nil. Otherwise, simply further attachment—You will have to take rebirth, either as a human being or as a demigod or as an animal, as a serpent, as a bird, as a beast. You will have to take birth.

So, this basic principle of increasing attachment is not our business, although it is the general tendency—griha, kshetra, suta [home, land, sons]—but if one can reduce and stop it, that is first class. Therefore our Vedic system is to first of all train a boy as a brahmacari—no sex life. The Vedic principle is to reduce attachment, not to increase it. Therefore the whole system is called varnashrama-dharma.

The Indian system calls for varna and ashrama—four social orders and four spiritual orders. Brahmacarya [celibate student life], grihastha [married life], vanaprastha [retired life] and sannyasa [renounced life]—these are the spiritual orders. And the social orders consist of brahmanas [intellectuals], kshatriyas [administrators], vaishyas [merchants and farmers] and shudras [ordinary workers]. So under this system, the regulative principles are so nice that even if one has the tendency to enjoy material life, he is so nicely molded that at last he achieves liberation and goes back home, back to Godhead. This is the process. So sex life is not required, but because we are attached to it, therefore there are some regulative principles under which it is maintained.