Is this considered cheating?

We were in a healthy relationship from past 4 years and managing household expenses together. He worked in corporate sector while I am a government employee. Things were going smooth until this day when I received a call from unknown number!

Usually I avoid attending such calls but due to the nature of my job I had to pick it up after a few missed calls thinking it might be from my office colleague or staff. It was a high pitched guy calling me by my name and claiming to have met at a recent exhibition while I didn't have a clue who h really was. I was confused about what he was up to and listened to him for a few minutes and ended the call ultimately.

Days passed and I forgot the thing but a notification from my social media caught my eye. He was the same guy from exhibition now making his way into my DMS. Saw his profile and somehow remembered he was a brother of my past colleague whom I had met few weeks ago at our office event.

He was bulky but seemed handsome and due to a common boundary we had a few talks obviously in limits. But things in my DM's seem quiet different when his talks escalated and he was pushing me to answer even when I wasn't interested as he knew I was committed but to my surprise I found out from a colleague that even this guy was in a commitment still searing such sneaks?

I tried communicating him how wrong we were and why were we going beyond limits but he seemed pretty cool with everyone and never accepted his commitment and stated he had no wrong intentions. Deep inside I had a strong feeling of how I might get caught some day or maybe questioned by my partner as we were almost always chatting and letting each other know what was happening.

Although my partner was very nice and understanding and he never accused me of cheating nor did I accused him of any. But that day was different!

I was in a hussle as I was late for work while my partner had an off that day so he was up but chilling on the couch where my phone and watch were placed. I had no idea that things can get soo nasty in a single moment. He called me for the very first time while I was with my partner gathering my stuff and my partner tried giving me my phone but I was too busy. Repeated calls made him PICK UP THE PHONE and that idiot without hesitation asked to come down quickly without hearing who it was from the other side.

My partner rushed towards the balcony to see who it was and found him staring in his new car. As soon as their eyes met he fled and leaving behind a big pile of questions for me and my ex partner.