Relationship between Macbeth and Banquo

From the beginning of the story, MacBeth and Banquo are good friends. They live equal lives because they are both thanes. I think they both like each others very much, they admire each other's strength and fighting abilities. When the witches made the prediction on Macbeth and Banquo, they did not believe on it at first, but when the predictions became true one by one, Banquo still acts like before, but Macbeth's mind is totally changed, which result of Banquo's death. When Macbeth became the king, he has to slay Banquo because he is the only one that knows about the truth. They became enemies and eventually, Macbeth killed Banquo. I think Banquo is pretty stupid to stay with Macbeth, i believe he is a smart guy, he should knows that his family and himself are in danger, he should run away with his family and never return.