My 35-Year-Old Sister Is Dating a 19-Year-Old, and I Can’t Even Look at Her the Same… Am I Overreacting?

I really need some outside perspective because I feel like I’m losing my mind over this.

A little backstory: My sister (35) has an 8-year-old daughter with a man who, from the start, our whole family knew was bad news. That relationship ended in flames, and during the breakup, she gained a following in the online “gun community” while also cheating on her husband with a guy across the country. She rushed into an engagement with him, even got a tattoo of his state, and—shocker—that also ended disastrously. My brother and I (we’re really close) were left picking up the pieces because my sister is wildly emotional and doesn’t handle breakups well.

Fast forward to now: She’s been into online dating for about a year, and some of the men have been noticeably younger than her, which has already been hard for me and my brother to watch. She was dating a 26-year-old for a bit, and even that felt weird, but now… she’s seriously involved with a 19-year-old. A guy who just turned 19 in December.

To put it in perspective, I’m 10 years younger than my sister, and he is 6 years younger than me. He is closer in age to her daughter than he is to her. And I just can’t get over how weird and wrong this feels. It gives me the massive ick. Like… what does a 35-year-old even have in common with someone who just graduated high school?? Not to mention, there is no way a 19-year-old can be a proper step-parent to her daughter.

She knows it’s weird, too, because she’s lied about his age to people. That alone tells me even she feels some level of shame about it. I just hate that she’s not thinking about her daughter right now. And honestly, I don’t even know how to talk to her anymore because I can’t pretend I’m okay with this.

Am I just being judgmental, or is this as weird as it feels? And how do I even handle this? Because right now, I feel like distancing myself from her completely.

EDIT: Just to clarify—I typically mind my own business when it comes to my sister, but it’s hard when she makes her business everyone else’s. I actually had to stop talking with her about this relationship. I was trying to be supportive. Our last conversation about it, she was obsessively checking his Snapchat score and asking him why it was going up even when they weren’t talking. That’s just… childish to me, and it’s part of why this whole thing makes me so uncomfortable.

Also, I want to make it clear that I’m still very much involved in my niece’s life and keep up with her as much as possible. One of my biggest concerns in all of this is how my sister’s choices affect her daughter. My niece is homeschooled by my sister, but unfortunately, that’s had a huge impact on her education—she’s 8 years old and still can’t read or write at all. I understand that some kids struggle with learning certain things, but I just wish my sister would get her the proper help instead of letting this go unchecked. While my sister is wrapped up in this relationship, there are way bigger issues at play that she’s neglecting.

My sister and I are very close. Our parents have passed so she looks to my brother and I for a lot of things, this included. She makes her life our life so sometimes it is hard to separate it.