I discovered Heather Gudenkauf about five years ago. And then as usually happens with me, author names got out of my brain as do titles, and so it wasn't until I saw her new novel Before She was Found came out, that I remembered, "Hey, she's that author that I liked so much whose name I forgot and titles I can't remember." I put my name in at the library for the hold and took out This is How I Lied while I waited. Both of these books focus on obsession, love, friendship...the stresses that can happen between best friends especially when a man is involved. This is How I Lied relies on flashback- the female character is much older now, a grown woman, married and expecting when her best friend's unsolved murder resurfaces. Before She was Found takes place in the moment, just hours after young girls' fascination with urban legends and their own insecurities takes them down a path they may never be able to walk back from.
Gudenkauf does a great job of straddling the psychological with the relational. Her characters are wholly flawed and three dimensional. The psychological pieces are well-defined and complex but realistic enough that you don't feel cheated by an ending you had no way of ever seeing.
She also has quite an impressive amount of written tomes (wonder if that word will ever show up on Wordle!), so if you are looking for books of this genre, give her a try. I'm sure you'll find some plot line that will peak your interest.