Hello community, i’m looking for a movie for my friend, she gave me following indications so these are the keywords you can work with:

Apparently, the movie is about young pair/couple (a people with age range between 18 and 20 approx.)

They are together for eight years.

But on the day at their anniversary, the guy will kiss his bestfriend girl next to the pool (having a party?) and the guy’s girlfriend will know it because she’ll find out by reading text messages in a guy’s mobile.

^ this one is complicated but i don’t know if i understood it well

Movie is approximately from 2011

Each one of the pair, never had anyone else before

These informations is all i’ve got from my friend who’s searching for the movie. Thank you everyone for your answers.