Friends murdered while stuck in house in woods

[Michelle]

Fairly new book I think. I have read it in the past two years. It takes place in modern times.

The main character is a girl. She and her boyfriend and other friend(s) are going on a trip to a cabin in the woods.

She runs into her male childhood best friend/neighbor outside one day and awkwardly invites him even though he doesn't like her boyfriend. He reluctantly agrees to come along too.

Someone ends up murdered, and they all start to doubt each other, and then at least one or two more people get murdered. The boyfriend and the male best friend definitely blame each other and she doesn't know who to trust.

It ends up being the male best friend that committed the murders. He even stabs himself to make it look like it wasn't him. He knew she would see him outside that day and invite him to the cabin and staged the whole thing. He only pretended to not want to go.

[Lobstergirl, au gratin]

Fiction or nonfiction? The genre needs to be in your header.