The Gatehouse Café by K.T. Dady

Vivien leads a double life. A happy one the world sees, and a miserable one that’s hidden away. Nobody knows what goes on in her home once she has closed up the café for the day. She doesn’t think anyone will believe that her partner is a horrible person, especially as he is a policeman.
Finn has been secretly in love with Vivien since he was a teenager, but she’s only ever viewed him as a friend. When he discovers she’s in trouble at home, he does everything in his power to help set her free, because even if she never falls in love with him, she’s still his best friend, and she needs help.