My best friend betrayed me or maybe not?

So this happened a few years ago. My spouse and I decided to separate. We had a lot of issues but frankly I did not think drugs and booze was a good thing. Granted he had a history before we met but I overlooked it and thought he changed. Alas, he went back to his habits and I decided to ends things. We agreed to separate and I planned on moving out. My best friend at the time knew about everything. She also knew I cheated on my husband. I should have waited until we were divorced officially or at least I was no longer living with him, I realize that. I am not a perfect person and made the wrong decision.
Here is my dilemma after all of these years... at this point I was about to move out. We separated our finances and agreed on how we will coparent. One fine day my soon to be ex husband confronts me about cheating and of course everything implodes. I found out that it was my best friend who told him everything. She also ended up making thing sup saying he needs a lawyer and to take my son away from me because I am an unfit mother etc. Then tells him i plan to take all of his money! What money..??? Anyways... to this day I do not talk to her. She knew the truth so I don't know why she lied to him and told him I was planning on trying to get child support or alimony. I never confronted her. She never talked to me again. But it seemed for at least 6 months after the separation she didn't want to talk on the phone or see me. Only talked to me in texts. She purposefully collected information and used it against me. I don't know why because she knew I was separated from him yet outted me. Of course after that a huge divorce and legal battle between me and my ex spouse ensued. Why did she do It? What did she gain? I wish I knew.... they still talk and have hung out several times. I am just not sure what she had to gain from all of this.... or did she do the right thing?