In the sense of continued survival of the specis, yes it is a need.
In the sense of continued survival of an organism, i.e. a particular human being, no. I am not saying it would be pleasant, but a human being can survive a normal lifespan without ever having sex.
The organisms make up the species. Extinction occurs when the death rate would exceed the birth rate. In some countries in Scandanavia this is already happening. On a long enough time line, the population would be negatively biased and be ill-fated for recovery, thus leading to extinction.
We have the technology and the wherewithal to prevent that, but that is only recent. VERY RECENT. For Hundreds of thousands of years, humans were teetering on extinction and many genus of Homo completely died out as a result. Homo erectus, Homo habilis just to name two of many. Keep in mind these species overlapped with Homo Sapien which is modern man.
What does this mean? This means that sexual desire is hard wired and so prevalent due to the neccessity of surival. It is Evolutionary beneficial that the organisms with the highest sexual urges and desires are more often than not, the most destined for the longest survival. Sheer numbers will ensure survivability. Sexual urge and desire are very important and arguable THE MOST important in any species for survival.
Given the long gestation period of human reproduction, and the few offspring we can produce at a time, sexual desire is quite strong as this promotes the species to have more, thus ensuring survival.
If any trait in humans made it this far, it is soley because in some way it is Evolutionary beneficial.