It is bad to cheat on someone who trust you.
Jonah has been dating Martha, who he has promised to be faithful to.
Jonah wants to date other people.
Jonah tells Martha he wants to date other people.
Jonah dates other girls behind Martha's back.
Martha accepts Jonah's honesty and moves on with her life while he dates other girls.
Martha finds out about Jonah's cheating and is never able to trust anyone again.