This is my very first post. I apologize in advanced if I don't know what I'm doing lol

For context, my ex bf and I had been on and off for 8 years. He recently broke up with me because I said hello to a male college classmate while I was on the phone with him. It turned into a big argument but I refused to apologize for saying hello to someone even if it was a guy. He claimed I was being rude from the moment he asked me my classmate, but I am CONFIDENT I remained calm up until the 4th question. He called me a bitch when I got off the phone and refused to apologize for that (I can explain this in detail but this is not the reason why I am posting this question).

Anyways, let me take you back to the beginning of our relationship. The first 6-8 months were great. Then, it started going downhill fast. He would constantly break up with me and I always chose to ignore huge red flags (blocking me on all social media for no reason, refusing to update relationship status from "single"-- even after 8 years of being together, refusing to delete exes/old hookups phone numbers, etc.)

On one occasion, he broke up with me for some months and I decided to respond to an old fling's messages. We met up a couple of times and did some stuff. Ex and I decided to get back together about a month later or so. I immediately cut off all contact with old fling.

Fast forward a year later (about 6 years ago from now), my ex goes through my phone and finds one message between old fling and I. Nothing inappropriate whatsoever but he hounded me about who he was until I confessed everything.

That led to 6 years of CONSTANT accusations from ex thinking I was cheating, lying, and being shady which is far from the truth.

Although we are broken up for good now, the question still haunts me. Should I have told him about what I did when we were broken up from the get-go?

EDIT: I am aware this is going to sound like an excuse, but I felt terrified of being honest with him because he had always been a super insecure person although he had no reason to be. He is insanely handsome, funny, and successful, among other things. From the moment I met him, he had a problem with anyone saying hi to me or even looking at me. I thought I was doing myself a favor by not sharing what I had done (and honestly felt like it was none of his business because he had dumped me) but it clearly bit my ass.