How do you be a best friend to someone you constantly get in fights with then become friends with again?

I have known this girl since third grade and things were fine until this summer. Friendships were lost with other people and I was attached as she was to me. We fight over the stupidest things but we always end up talking to each other again. Lying always gets to be a part of the fight and the past does. I want to know how to get rid of this situation and just being able to have a true relationship with this girl. We dated over the summer which started this whole thing and...How do you be a best friend to someone you constantly get in fights with then become friends with again?
a relationship w/o a fight is not perfect. thats one way to prove to ourselves that we are friends, mo matter what mess we end up on, no matter how much we fight, we still find that friendship in us to tell us to see beyond our differences and just be ok w/ each other again..