![](https://cdn.mamamia.com.au/wp/wp-content/uploads/2016/04/06145128/affair-MM1-600x456.jpg)
Being cheated on is horrible under any circumstances – but if your partner cheats on you with someone close to you, it’s almost unbearable.
That’s the situation a 26-year-old US woman has found herself in recently, after she discovered that Jake, her 28-year-old fiancé, had slept with her emotionally unstable sister Sara.
And the icing on the cake? Her mother knew the whole time, but didn’t tell her.
Ouch.
![fiance cheated](https://cdn.mamamia.com.au/wp/wp-content/uploads/2016/04/06145128/affair-MM1-600x456.jpg)
The woman, known only as brokenheartedsister, has told her sad story on Reddit and had pleaded for help in moving on.