My “best friend” fucked my ex ....?

So awhile back, about 2 n a half years ago maybe I broke up with my ex, of 5 years. I loved him and I always did but we were to toxic towards each other. Fast forward to today, my supposed friend of like 12 + years fucks him.

And mind you she hated him our entire relationship. Despised him. Always talked shit about him. Always made fun of him. Always said he’s ugly and so on and so forth. Me and her have been friends since I can remember. We kinda went our separate ways the last year and a half ( I got into a new relationship ) and was always busy and working and never had time to talk or hang out with her and she always said it was fine at first but soon enough she started being rude, short answers blah blah blah. It was whatever I knew she would always be there for me if I needed her.

She messages me and says I’m gonna go ahead and remove myself? And I’m like what? So she deleted me off Facebook, re adds me, I ask her wtf and then she deleted me again. Doesn’t even have the balls to tell me she sleeps with my ex. I’m sure I’ll get hate saying well you guys aren’t together anymore why does it matter? That’s not really he point. That was someone I put time and effort into. Someone I gave things up for. He should never be fair game, no matter the circumstances. In my opinion. But, I’m actually not even mad. It’s hilarious really. But should I be mad at my so called friend? It’s just weird.. OH and she cheated on her ex who was actually my exes best friend like a trillion times and I always a good enough friend to never tell anyone. This is why I don’t have any friends. Lmao