A surprise ending for my story ?

I've written a story about a girl who has ano affair with her best friend's boyfriend. I know it sounds cliche but their relationship, characters etc are not cliche at all. Now i just need an ending, I want to end it with a twist, but nothing too far fetched, just different than how a love triangle story usually ends. I've tried to end it with happily ever after (the best friend finds out, freaks out at first but accepts it eventually) and I've tried to end it with the guy going back to his original girlfriend, but somehow none of them felt right. How would YOU end it ? Thanks in advance :)