SB 11.3.18
sri-prabuddha uvaca
karmany arabhamananam
duhkha-hatyai sukhaya ca
pasyet paka-viparyasam
mithuni-carinam nrnam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Sri Prabuddha said: Accepting the roles of male and female in human society, the conditioned souls unite in sexual relationships. Thus they constantly make material endeavors to eliminate their unhappiness and unlimitedly increase their pleasure. But one should see that they inevitably achieve exactly the opposite result. In other words, their happiness inevitably vanishes, and as they grow older their material discomfort increases.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Without the mercy of a pure devotee it is exceedingly difficult to free oneself from the bodily concept of life, which is the illusory basis of sexual attraction.