Whenever someone's gf acts out of character or does something really awful to their now ex, I hear people saying left and right that "If someone treats you like that, they never loved you in the first place."

What do you think about this? Is this just an example of briffaults law? As soon as her emotions stop she doesnt give a shit about you as a person? Or did she never really love you? In that case people send years with people that dont love them.