How someone dare to say love?

I have once before, yes. My friend said she loved her boyfriend constantly. They dated for about a year and broke up once during that time. She cried and said she loved him and all that jazz and they eventually got back together later because they 'couldn't live without eachother'. A few months later, she met somebody else and, in a matter of a day or two, left her boyfriend for him. She wasn't sad, she didn't feel guilty, hell, she ended it and didn't seem to care at all. It was him who was depressed and she found that odd. It really shocked me. How could she claim that she loved him for a year and then leave him so easily? Some people out there..