I dated someone who was a pathological liar. He would lie about what he had for breakfast. He'd lie for no reason at all.

People with the 'dark triad' of personality traits will often push the boundaries of acceptable behavior. I don't know if anyone really understands why they do this, or even if there is a 'reason' in a conventional sense. That was my last relationship and although it was difficult and painful to get out of I am so relieved not to have to deal with all the bs all the time.

I hope you also find peace.