I caught my boyfriend talking to a girl in another country

I caught my boyfriend talking to a girl in another country. For some context, i have been with this man for 5 years. We have had our ups and downs as all relationships do but never did i think it would lead to something like this.
Our relationship has been so good, or so from what i thought. I am the kind of person that has so much love to give but recently i haven’t been getting it in return from my partner. We went to a concert recently and had a great time, got dinner afterwards and headed home. I was in the room and he was doing his own thing in the kitchen, i got up to go check and as i did so i found his phone on the ground. I picked it up and found a discord notification from a girl, me being his girlfriend of 5 years, i sit down and i open his phone. I clicked on the notification and was immediately introduced to a whole conversation he has had with with woman for about a month and a half. She never once showed her face, nor her body, she even explained how uncomfortable he made her at one point because he asked if she was a “bad girl.” They still proceeded to talk afterwards, conversations grew more intimate and intense with one another. They met on a video game, and from the conversation it seemed as if this woman fell in love with him through the video game. As i am reading this and recording for evidence, my hand shaking, quite literally let out a death scream. My boyfriend, then comes running to where I am at because he is concerned, and when he arrives, I let him know that I found out what he was doing on his phone.. and his immediate response was “was this planned?!”, He sat there and watched me cry in silence. I went home, did not talk to him for a few days. And he calls me sobbing begging for my forgiveness. The sad thing is, he could not own up to it. He was sorry because i found out. This woman lived in Korea, she could have been a catfish, most likely was. I don’t know what to do, i love him and my heart it telling me to forgive but its also telling me to walk away.. its just hard to walk away from someone you have spent so much time with, someone you love, in the past 5 years.