"is" and "was" in the same phrase: What is the tense? Past or present?

Question

I've come across with the sentence below:

that its not affecting me, that was its effect.

I've lost the tense of sentence. Is it past or present?

The full text is here:

As if he could read my mind, he twisted my wrist further; my body was coiled tightly, my face scraping the floor. I’d done all I could do to relieve the pressure in my wrist. If he kept twisting, it would break.

“Apologize,” he said.

There was a long moment in which fire burned up my arm and into my brain. “I’m sorry,” I said.

He dropped my wrist and I fell to the floor. I could hear his steps moving down the hall. I stood and quietly locked the bathroom door, then I stared into the mirror at the girl clutching her wrist. Her eyes were glassy and drops slid down her cheeks. I hated her for her weakness, for having a heart to break. That he could hurt her, that anyone could hurt her like that, was inexcusable.

I’m only crying from the pain, I told myself. From the pain in my wrist. Not from anything else.

This moment would define my memory of that night, and of the many nights like it, for a decade. In it I saw myself as unbreakable, as tender as stone. At first I merely believed this, until one day it became the truth. Then I was able to tell myself, without lying, that it didn’t affect me, that he didn’t affect me, because nothing affected me. I didn’t understand how morbidly right I was. How I had hollowed myself out. For all my obsessing over the consequences of that night, I had misunderstood the vital truth: that its not affecting me, that was its effect.

Answer 1

It took me a couple of readings to understand this.

Note the first part is "its not affecting me" and not "it’s not affecting me". That word isn't "it is" but the possessive form. That first part means The fact that it didn't affect me".

Now the whole phrase makes sense:

*That night changed me. It affected me. It had an effect.**

The effect was I can no longer be changed by bad things or I can no longer be affected by bad things.

Or The effect of that night was the fact that it didn't affect me. Which is shortened and rearranged to "its not affecting me, that was its effect."

I suspect the author is purposely playing with the similar sounding words "affect" and "effect" here.

The phrase has only one finite verb "was" and is past tense (to fit with rest of the narrative).