You should tell your partner you want to leave them.
Phoebe wants to try out a new relationship.
Phoebe wants to break up with her current boyfriend.
Phoebe is open with her boyfriend and explains that she doesn't love him anymore.
Phoebe sleeps with her boyfriend’s best friend and makes it easy for the boyfriend to find out.
Phoebe's boyfriend is devastated, but understands, and ultimately accepts it.
Phoebe's boyfriend dumps her, and tells everyone who will listen about what she did.