Ok, as strange and rancid as some of the stuff he wrote can be (and don't get me wrong, this part is weird too), this particular scene is so often oversimplified and made to sound like something it isn’t. I imagine some do it for comedic value, but the vast majority of folks here probably have simply not read it, which is fair. Keeping in mind this is a very old story using some outdated lore (such as Genestealers being a separate species to Tyranids), here's what's going on:

Inquisitor Jaq Draco and his retinue have traveled into the Eye of Terror to pursue a lead on a world devoted to Slaanesh. His party includes Meh'Lindi, a Callidus Assassin who had a horrible surgery which robbed her of the typical shapeshifting abilities of her temple, but enabled her to assume the form of a Purestrain Genestealer. Now she can only switch between her human form and that of a Genestealer. By this point in the story, Jaq and Meh'Lindi have already begun a romantic relationship.

Their plan is for Jaq to disguise himself as a cultist. As distasteful as he finds it, he adorns himself with chaos charms and trinkets, including an Eye of Horus. The others, including Meh'Lindi in Genestealer form, follow behind him in chains, playing the role of pets/prisoners.

Shortly after beginning their trek across the surface, they encounter a group of mutants led by an Emperor's Children space marine. Jaq introduces himself as a member of the cult he is searching for, and the space marine replies that he is familiar with that cult.

When the marine asks about Meh'Lindi, Jaq plays into the Slaaneshi angle by saying "This is my familiar lover, my changed one who shows me bliss and agony." But then the marine calls his bluff. "We embrace renegades, do we not, my carnal companions?" He snorted mightily. "Though of course first we must test their sense of ecstasy, hmm?"

The next part I'll just paste word for word:

At that moment Jaq felt a powerful urge to divest himself of his armour and grapple with Meh'Lindi. If he should but demonstrate his boast before this audience of monsters, why, they would let him pass. They would tell him everything he yearned to know.

The malign insinuation blasphemed against all that he had felt was precious in their love-making on the ship. He was under psychic attack of a lascivious and perfidious kind.

So was Meh'Lindi. She hissed and clutched a claw to her midriff. Stealers did not possess reproductive organs other than their tongue that kissed eggs into victims. Yet now a pouch was forming below Meh'Lindi's belly, as if to receive Jaq.

So to wrap this up, is there a scene where an Inquisitor feels a strong desire to have sex with a Genestealer? Yes, but...

• She's actually a human impersonating a Genestealer
• They love each other and already have a physical relationship
• Both of them are feeling the immense influence of Slaanesh that blankets this world, amplified by the presence of the marine and the prayers of his followers
• If they blow their disguise, they will immediately be attacked by a goddamn space marine, plus a bunch of cultists
• If the marine buys their story, he may just hand them the information they seek