Why "best friend" is so much a "best enemy"?

I wonder sometimes. But I think they both just want to prove to themselves that they are better than each other. They copy what they find good about the ex-girlfriend, without admitting it. Both seek other friends, they draw on their side and then goes to the terrorist stress really begins. That's life.

I think it's because you can release the better .. if you really are best friends, then you would really do anything for each other. But when you suddenly realize that you begin to live apart, it is usually very sad and then you find it easier to disperse in the dispute, even if you will not see that often.

because many best friend know exactly about us they know exactly about ourself, our family, our motivation, our live. just one thing and make our best friend become our greatest enemy