Raven is constructed as someone who is in control his emotions, that doesn't mean he is asexual
Think him as a human cat

I think as played/directed he was just 'anti-social'
As much as I love Noir one of the problems I find with the Hays-code era projects is that the culture has changed in the 70+ years to the point that it's hard to distinguish between writing around the Code; being vague for the sake of Audience interpretation vs loose threads from editing (apparently there was over 10 minutes cut from the original version, some of which was flashback or prologue showing young Raven with the aunt
IF one were to remake/adapt the film in Modern Hollywood they'd crank the dial in one direction or another:
A show the nature of the abuse from the Aunt to make him clearly Asexual or
B make him a memetic sex god who'd seduce Ellen away from her cop-bf and escape with her at the end

I agree, Out-of-Towner, about not having any friends. However, he can be asocial and asexual because of his horrific childhood. He does thaw to Veronica's character, though, by the time she gives him a kiss on the cheek. The first time she touches his shoulder, he almost reacts as if he had been burned and it hurt. He had built up such a protective shell, and he didn't want anyone to penetrate itrelationships equaled pain, from his experience.

I think a better term to describe Raven would be asocial, not asexual. As you mention in your post, he doesn't really warm up to anyone, female or male. He doesn't have any friends. He never allows himself to get close enough to anyone to even consider having sex. The only living thing he can relate to are cats. Why cats? As Raven says: "Their on their own. They don't need anybody."

I didn't find his character to be asexual. His life meant that he couldn't keep the normal attachments we take for granted.

Stripping under the name Malcolm Sex, I pleased the ladies by any means necessary.

Raven seemed sort of asexual by force of will. When he focused on survival and keeping his emotions at bay, he had no lady friends, as he told his slimy employer when the man brought up the concert tickets. However, he seemed to be sexually flattered by Ellen when she held him and kissed his cheek. I get the feeling that he was at least a little bit interested in her but when she comfirmed that she loved and was going to marry "the cop," he discounted any real romantic or sexual relationship.
Also, a man in Raven's line of work who seeks revenge might never come home. Even if he could control his temper, he knows that he is not stable enough to give a woman a real life with him.

What female lover? I don't remember him having one.
I don't recall him seeing anyone from the boarding house either. The only girl I remember there is the one he terrifies and whose dress he rips for scaring the cat.
And Darkness and Decay and the Red Death held illimitable dominion over all.

spoliers below!
didn't he kill his female lover? And hadnt he been seeing the lady from the boarding house/motel?