Because they have sex. But really either because they really love each other or that one of them just wants the other for sex.
Girls have boyfriends because boys can easily get boyfriends just like how girls can get girlfriends so girls get boyfriends to prevent boys from getting boyfriends and girls from getting girlfriends.
There are no boyfriends and girlfriends on Moshi Monsters.
They love their girlfriends that much
love
boyfriends/girlfriends!
usually they are friends
Sometimes they blackmail there girlfriends to stay with themor they like bashing there girlfriends up.
not old enough!
if you want to
It is a day to celebrate the girlfriends with loving and caring boyfriends and the hard work the girls do.
Jealousy
if it's your girlfriends or boyfriends if your a girl