I read a book about 10 years ago, not sure if it was released then or earlier. The main character is some kind of TV presenter, her husband has an affair with a younger woman named Tessa. Tessa ends up working at the same TV station as the woman.
The woman's best friend end ups brutally killed at the end and I think it was suggested that it was Tessa who killed her.
If I remember any more details I will post them. Haven't a clue who the author is or the name of the book so not much to go on - sorry!
Hopefully someone will know it because it's driving me crazy!