Why did my ex-boyfriend deny he sexually harassed a woman, despite his history of sexual assault on other women?

Because that’s how abusers roll.

This is a sexual abuser’s standard operating procedure.

Since rape culture works to give rapists, flashers, ass grabbers, molesters, and harassers social license, they can hide in plain sight and continue to do the thing they like most: sexually abusing people (usually women).

Notice what this serial rapist has to say about it.

Some of them were into it, and those nights were usually consensual and boring sex, sometimes followed up by a few more nightly visits before getting the boot. However, the great nights were the ones who squirmed, ones who didn’t want to give in. …

To be honest, even remembering it now, the squirming always made it better, they didn’t want it to happen, but they couldn’t do anything about it. Most girls don’t say no either. …

I never worried too much about being caught. Everyone knew me, and I worked with the police a lot, with administrators, and campus officials. I was on first name basis with the Chancellor and the President of Student Affairs, so if anything came down to a he/she-said I figured I’d be in the clear. Having her come over to my place also made it seem less predatory, as she came into my domain, and “could leave at any time”.

Your sexually abusive ex-boyfriend is going to ride the denial wave until he gets cut up by the coral reef of truth.

You don’t have to be the coral reef. Just notice how often he runs into it.