My ex-husband and I split about 2.5 years ago in a somewhat tense divorce, but we are "amicable" now, in a sort of frenemies way. I initiated the divorce, and I have been nothing but patient and empathetic the entire time, giving him space and trying to have a pleasant relationship for our two young children (one is a preschooler, the other is an elementary schooler, I don't want to give exact ages for anonymity). We have 50/50 custody, which I am not thrilled about.
He is a narcissist with undiagnosed bipolar disorder (it runs in his family heavily, but obviously he won't get a diagnosis ever). I am not a doctor, but he checks all the boxes and makes our lives very difficult with his unpredictable, volatile nature and manic episodes. Clinical bipolar or not, he is a very difficult man to be around, and in recent years has fallen victim to alt-right politics, although that's another post altogether.
Since he's starting dating again (pretty much as soon as I walked out the door when we separated) I've been encouraging. He hasn't been serious enough with any of them to introduce them to our kids, but he's been with the person in question for several months and decided to do so. As per our separation agreement, he invited me over to introduce us.
I was more than happy to meet her (I welcome any distraction that gets this man to leave me alone) and even offered beforehand that he could give her my number in the event all three of us needed to communicate about the kids. She and I exchanged a few pleasant texts, and she seemed normal, although my ex had implied she was a college student. I figured "pfft, typical," because he's been dating ~10 years younger since we split, but whatever. I would be thrilled for my children to have another caring adult in their lives.
When I went to meet her, we were having a nice conversation when I asked what school she went to, as there are a few colleges nearby. They looked at each other awkwardly before my ex said "Uh... she's actually... finishing up her last year of high school." I was floored. I tried to stay normal for the remainder of the visit, but I've been going through it ever since.
I have been back and forth in a million ways since then. I've regretted not saying something in the moment, I've felt as though I should leave it alone, I've cried over this girl and how he has groomed her and taken advantage of her. I've spoken at length to friends and family about what to do with many mixed responses. I can't tell if she's 17 or 18, but in our state, the age of consent is 16 so I'm pretty sure this isn't illegal if she's a minor. She actually followed me on social media and, my god does this girl have it rough. She's blatantly posting pictures and videos of her and her friends drinking and getting up to all sorts of things. While I didn't expect my ex to be so disgusting, I'm not even really upset with him. I am just completely devastated for her.
It's worth noting that my kids have met her many times at this point, with my eldest having a fondness for her. They said they do homework while she does "college" work, so I know my ex-husband has lied to them about her age. They seem to enjoy her company so far, and I absolutely never ask about what goes on at "Dad's house," so this is all information they tell me of their own volition. I work very hard to talk positively about my ex-husband to my kids.
Should I find her parents and tell them anonymously? Or should I leave it alone and count on this not lasting? If I were this girl's mother, I would want the woman in my shoes to do something. I know with absolute certainty that her parents don't know she's dating a man almost double her age. I don't know if his family knows, but most of them hate me since the divorce, and even if I told them with the intention that they'd put pressure on him, I don't even know if that would accomplish anything.
I am having a hard time finding an outcome that won't damage my relationship with my children's father, because it has only recently been tolerable. I'm also a little bit afraid of my ex, because while he wasn't violent in our marriage, he became more and more aggressive and he's just completely unpredictable now. I would be admittedly a little fearful if this pointed back to me. She also said she's going to college next year in another state, so this relationship could be temporary anyway. That's not to say there won't be more teenage girlfriends in the future, at least.
What should I do? Thanks for reading. It's been a very stressful few years and I'm very tired.