AITA for telling my parents about my sister’s infidelity with update and context?

DexWest
So, 2 days ago, I made a post asking the same question and realized I should have give more context and the backstory. Sorry, I read posts like these. Never thought I’d be making one. lol.

My sister called me and told me that she met a new friend. I told her congratulations and then she told me that she slept with him. When I asked why, she said that they click and he just gets her. That she’s never clicked with someone like that before. I asked how they met and she said it was 5 days ago at work, but he’s only here for business cause he live 5 states away. I asked if she told my BIL and she said yes. I asked her what she was going to do now, and she told me that she was thinking of divorcing him because, “she loves him, but isn’t in love with him anymore.” I asked what caused this and she said a lot of trivial things such as that he put on weight. I told her that this is where her marriage actually begins because it’s not about the times that everything is going well, but when you want to smother them in their sleep. That it’s not about her anymore. She also has her son to think about because we all know about how children develop in a fractured household. She replied with “I’m not going to stay in a relationship if it doesn’t make me happy just because of a child.” I asked if he’s violent, abusive, is she in danger? She said no. It was only that she wasn’t attracted to him anymore. So after a few more comments and requesting she keep me updated, I called my mom to vent because I’ve never heard someone be so shallow and conceited. It was my goal to hopefully have my mom knock some sense into her.
Update 2: my sister cut off contact with me because I had no right to tell my parents about her infidelity because she had no intention of telling them. No contact since.
AITA for telling my parents about my sister’s infidelity with update and context?
4 Opinion