Yeah, but that sexual impulse is not limited to the physical plane and physical bodies. The sexual impulse comes from an exchange of male and female energy, which you have on the astral and higher planes as well.
In deed, astral sex and energy exchange takes place all the time, even on the physical. When two auras meet it is already happening. That magnetism between a man and woman, even if they do not touch each other, sexual energy exchange is already taking place via their auras 
Lust can also be expressed in a totally loving way, e.g. Tantra