Nettie needs our book help! Oh boy this one sounds tumultuous. LOVE TRIANGLE with 2 sisters and one guy? Eeeeep! That’s a recipe for disaster, and this description below goes into plenty of detail.
I read a book 15-20 years ago.
It’s about identical twin sisters and the “evil twin” tricks her sister’s boyfriend and sleeps with him and gets pregnant.
The “good sister “ leaves and gets a call several years later that her sister has cancer and is dying so she comes back.