My ex (she/they pronouns) is an alcoholic, frequently drinks and drives, makes dangerous impulse decisions, is a poor communicator, has commitment issues, has admitted to lying to my face, has blamed me solely for conflicts, has found ways to convince me of staying when I wanted to leave, gotten mad when I had opinions different than theirs and, worst of all, knows all of this and doesn't want to change. Theres also more but how could I possibly list all their red flags.

They don't want to hurt others, but they don't care if they hurt themselves, which then puts people close to them in danger.

she's dating someone new and I didn't say anything to her new girlfriend cause it isn't my place. But her new girlfriends best friend, who I've hooked up with, just reached out. She had a suspicion my ex was danger, and she was right. She now wants me to warn the new girl.

Like I said I don't feel like it's my place. But since she's dangerous, I also think her new girlfriend should be warned. what do I do??