Relationship and best friend code

Ok so I have a small problem if you can call it that, it just bothers me sometimes.

Time: (7th grade), So my best friend of 8 years has always been by my side and I love her but there’s one thing that always gets to me, it’s when she broke a best friend code. So it was my first relationship and we dated for 6 months. We sadly broke up but I wasn’t heartbroken because we just lost feelings and stopped talking.

6months later I found out from my other best friend that there was a problem. I can’t thank her enough for telling me this and shows how loyal she is.

So she said, “So I’ve been sworn to secrecy on this and have been keeping it from you for a bit, but I can’t stand looking at you without telling you any more. (Best friend #2) dated your ex right after you broke up.”(Like that day legit.) anyways I’m so glad she told me but I’m not mad that they were together, I’m just pretty mad about how A. It was that day meaning they had feelings right when we were dating and B. She broke the bestie code and lied to me for 6 months+.

Now that I think back, I should have seen it coming, they talked even more than me and him did, and SHE WAS THE ONE WHO TOLD ME HE WAS GONNA BREAK UP WITH ME!! Liek tf??

Idk I think I’m just asking for help with this situation because it still bugs me how she lied to me and acted like everything was fine when I partially/subtlety confronted her about it. and I’m going into 10th grade now.

Can anyone relate or help me out with opinions?