So I posted this on r/tipofmytongue almost three weeks ago. People tried to help but unfortunately I didn't have any luck. I even tried using a link somebody gave me to search through a catalog but couldn't find it. Starting to feel crazy lol. Apologies in advance for the weird formatting. My phone is being super weird today. For starters I'll paste my original post here:

I don't remember much about the book. I read it 2016/2017 so at least as old as that. Pretty much all I remember is that the main character was a high school girl whose brother was a school shooter. I think he died either by shooting himself or getting shot by the cops.

The only other part I remember is her brother had a best friend who the mc bonded with and had a romance throughout the book with.

I mentioned it in a comment on a different post and now it's driving me crazy that I can't remember it lol. Thanks for the help!

Also, I'd like to add something i said in a comment on my original post but major spoilers for the ending. You've been warned. The book ended with the main character and the brother's best friend deciding to end their relationship because they were just using each other as a safety net in the aftermath of their shared trauma.

The final thing I'll add to this post is a list of books that were already guessed on the other post to save you guys time. :)

Aftermath by Kelley Armstrong

Quicksand by Persson Giolito

19 Minutes by Jodi Picoult

Hey Nostradamus! by Douglas Coupland

ETA: as far as I remember, the shooting happened either at the very beginning of the book or before the book even started.