Title says it all really, but I will provide some background information.
My sister is 35, I am 25. I am closer to my brothers, but when I was young she used to babysit me a lot and often took care of me (paid), so we are kind of close. Probably a bit closer than average siblings with a big age gap. I love my sister dearly, but she can be difficult. She’s always had this thing about me being the favourite and my dad never loved her, and sometimes I get a bit sick of hearing about it. Other than that she’s overall a nice person (well I thought she was, this is making me question it.)
Today I went to lunch with her. She seemed excited and happy which was great since she has been a bit down recently. She was telling me about her new boyfriend and all was good. I suggested she brings him to a party I’m hosting in June and then she told me she can’t because of who he is. Long story short he is someone who works for our brother who is married.
I don’t know his wife super well but I know her a bit. My SIL is pretty good friend with her as well.
I didn’t really dig around about how this happened or anything because I was in shock. I told her she needs to stop this before it’s too late (I actually think it’s already too late if I’m honest) and left. She has tried calling me but I don’t want to talk to her. I wish she had never told me. I also think it’s really fucked up because she seemed almost happy about it? I am really unsure what to do because while I am not friends with this woman, but I feel really bad for her. This is out of character for my sister, so out of character that part of me wondered if she is having some kind of mental health episode? But I think that’s probably just me trying to make excuses for her. I also don’t want my SIL to hate me when/if this all comes out because I really like her.
The only other person I’ve told is my partner, and to be honest I didn’t really want to tell him I just ended up telling him because when I came home he knew something was wrong. He says I should stay out of it and that I should just wash my hands of my sister for a while at least.
I kind of just need to vent because I’m freaking out but if anyone has any advice I would really appreciate it.