Lies and more lies

My boyfriend and I were together for two years then he suddenly left me. No indication he was unhappy or anything. A few weeks later he can back begging saying he didn't know what he was doing. 
I decided to give him another chance and we've been seeing each other for around 6 months now - not officially boyfriend and girlfriend yet. He's been trying to prove to me that he's serious about me. 
Everything had been going fine apart from lies he keep telling me. Really silly stupid lies that are no big deal. I've spoken to him 3 times in the past week and he has still been doing it.
Then at the weekend his friends mentioned about his car and why he didn't drive today. Now I know he can't drive, nor does he have a car.  So it's not just me he's been lying to. 
Any help/advice would be appreciated! What do you do with a liar? Especially when trying to rebuild trust?