Should I have contacted her?

My ex and I have been hooking up for a couple of months now. I have him blocked on everything except WhatsApp. He told me that he and his girl (he went back to his bm after I broke up w him) had officially broke up. Turns out that’s not true…

When I found out (2 days ago) I messaged the girl to let her know. Told her he has been looking for me since February and to please make sure he does not bother me anymore. (I didn’t go into detail saying we have been having sex etc. It felt like too much or she was going to feel I was fighting her for him which I am not.)

She didn’t reply. She then changed her profile photo to sticking the middle finger out. I thought it was dedicated to me but I didn’t put much mind to it. Somebody who has my ex on whatapp (I have him blocked now) told me he posted a photo with his girl (babymother/ex wife ) today. So her profile pic was dedicated to me. And he posted that probably to make sure I see it (but he knows I have him blocked)

Back in Oct he and I had a terrible breakup. In which I discovered he was still playing family while being 2 years with me. I let her know hey this guy has been playing us both. Conversation went well until he made me seem like a liar and if I had made it all up. She believed him. She proceeded to make statuses, TikToks about me, make him her profile photo, put him in her bio. She even kept coming across my street and my gym. Keep in mind she lives far away from me but she wanted to make sure I knew she was around me lmao.

Fast forward putting that behind. I realize again he had been playing us both. And after everything she did I still decided to be kind enough and let her know. Yet she still doesn’t believe him. And dedicates me photos sticking the middle finger lol

Am I in the wrong for letting her know?

He got away with it the first time. And he’s getting with it again. I have decided to cut him off completely he’s a liar, manipulator and narcissist. But I can’t lie it bothers me he has proceeded to lie and cheat on women and has gotten away with it. Could be she refuses to believe he’s capable of such thing or she just knows it and is ok with him cheating.