Fabricating a pregnancy scare is lying.
Katie has been fighting with her partner frequently and is worried about their relationship.
Katie wants her partner to stay with her.
Katie takes note of the issues in the relationship and works hard to control her end of them.
Katie tells her partner that she is pregnant even though she is not in order to get him to stay.
Katie's partner notices her efforts and is motivated to stay with her.
Katie's partner finds out and this is the final straw for him.