AITA for responding to the message?

So ex and I broke up few days ago. Some history we have dated for about a year but broke up back in March when she left me for another guy and got back together in June. Both times she needed to work on herself to be better for me etc etc. She still texts me and sends pictures. We’ll yesterday my for you page showed an account I don’t follow. I click on the profile and It’s a guy I don’t know with her in his arms saying “you’re the only one I need” something cringey like that. So I sent that to her asking her what’s up? Her response was that’s her best friend and she sticks behind her not dating anyone and working on herself.. Few hours later I get a message on a burner account. Telling me to stop texting said ex. I asked who this way and we just broke up and everything was good until earlier. The person goes wait what? When did y’all break up etc. Apparently they had been talking for awhile being flirty and he thought he was dating her. long storey short it turns out she was playing both of us. I let this happen twice. Except I caught it the second time by accident. The new guy and I basically had a bro moment of sharing everything and breaking down what was going on and dates.

Part of me wishes I never replied to this random account. But I feel like I helped ghat dude dodge a bullet also considering her mother messaged me who I’m close to asking what was going on pretty much sums up she was breaking down getting caught in her lies and manipulation. I just hope they realize to stop doing this and hurting people. They need a ton of mental health help and I wish the best and they find it.