Can anyone give me advice on my confusing breakup? Why did my ex go to the girl he told me not to worry about?

I hope that everything I say will make sense. I will be using fake names to ensure privacy.
Let’s say I am “Rachel”, my ex-boyfriend is “John” and the side-girl is “Emily”.
John and I began our relationship almost three years ago. However after the first 10 months we broke up because I found out he had kissed someone when he want back to his hometown. After a bit he met Emily and had a thing with her for 3 months and dated her for three weeks, but than realized how much he missed me and begged for me back again. I gave in the second time because I felt like I could trust him. We were together for almost two years after that. We had an amazing relationship, we were best friends, and I know that he really did love me. However, there were moments where I questioned my trust towards him. John changed Emily’s name on his phone just so he could have the option of texting her at any time. When I confronted him he said he felt guilty and felt bad for her.
In March, we had to start a long distance relationship (due to corona) because we’re from two different countries. It was difficult but we managed to keep our relationship for another 6 months. Five days before he was supposed to come back (uni started) he broke up with me, out of nowhere and with no explanation.
We have been broken up for 3 months now and he won’t even say my name, he won’t talk to me. All I wanted was to talk to him so that we would be on good terms, but he just ignores me. And to make things worse, he is with Emily again.
Why when he was with me did he felt guilty enough to continue speaking to her, And why he avoids me and feels no guilt? I know that what they have isn’t strong, he doesn’t truly care for her. John and I live in the same city but Emily doesn’t, so they barely see each other. I know that John is very lost , I just don’t understand why.
I also want to clarify that I was 100% loyal.
Could anyone shed some light on John’s behavior, if he hates me and any other advice? Thank you
Can anyone give me advice on my confusing breakup? Why did my ex go to the girl he told me not to worry about?
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