You operate under assumption she was truthful to you. When actions and words do not add up usually words are lie.

Talking on about how her life is sad is standard procedure for certain type of girl. Those that are trully sad stay silent about it. In core some girls play damsel in distress and fish for hero,savior. Nasty bunch those.
Of course she won't tell you truth, they know how guys would react. Sometimes it is not case, but usually any kind of break. Any kind of i am not interested then she later on comes back- actually is just her thinking something may work out with another guy.
It does not work out so she goes back to what she thinks she can get.
You.
Here is reality it may be hard for you to accept but you aint all that important to her. You are not the event,person that will make her life happy or sad.
For her life and her happiness she is that person.

Your emotions are playing you, we all want to feel desired so we are prone to lie to ourselves. Distrust yourself for second. I claim that if she was so into you, there would be needed way,way more than misunderstanding for her to get her claws off you.