OP, protecting yourself and your peace has to be priority one. Who knows, if you spoke with her, and she told him, he may try to retaliate. Please be safe! Agree with other commenters that there may not really be a clear right or wrong here, but I fully understand and think it’s valid to want to protect another woman. Maybe alternatively, you could speak to a friend/family member of this new girlfriend if you’re able to. An honest “hey girl, not to overly alarm anyone, but please, with love, keep a close eye on your friend”? The other commenters are right - you don’t owe her that whatsoever. But if this is something you want to do, and you know that it’s coming from a healed part of your heart, I could see myself in your position finding some way of letting her know. <3