My best friend is dating my ex

Me [21M] and my ex boyfriend[21M] were together for a bit over 3 years. We broke up 3 months ago, and just a week ago I found out that one of my best friends (who I have hung out with during this time) has been dating my ex for about 2 months now. So yeah, they started dating ONE month after our breakup and he has kept it from me.

It is extremely hurtful and humiliating. I don’t understand how my ex could move on so quickly as if I meant nothing to him. We had a wonderful relationship and he meant so much to me. I helped him through so much and he was so grateful for everything. It was my first relationship and I gave him my all, and now he replaces me just like that. It seemed easy for him. Treating me like crap. He said:

“I felt i couldnt let my life choices revolve around not hurting someone who wasnt in my life anymore”

Then I pointed out to him that we had texted about maybe being able to be friends in the future, just before they had started dating. And I told him that he must have decided to forget about us saying that, so that he could justify dating my friend, and he AGREED.
So he was ready to forget about me completely, and treat me just like the toxic people he hates, treat him.

And my friend? He must have known that this was going to make our 6 year long friendship end. And he still chose to throw that away just bc he had a little crush.

I am barely comprehending that this has actually happened. They are barely showing any remorse and it is breaking my brain. I can’t understand how two people that I trusted so much could do this.

Please just send some hearts or something in the comments. I don’t have a lot of friends to talk to about this and it’s making me go insane. I just need to feel some sort of support. Thanks <3