How has Macbeth and Banquo's relationship changed between Act 1, Scene 3 and Act 3, Scene 1?

In , Scene
3,andare clearly good friends. This is the scene where the two men encounter , who prophesy
thatwill become Thane of Cawdor and King, and that Banquo's sons will become kings. Referring to
Macbeth as "trusted home," a term of endearment, Banquo urges Macbeth not to place too
much stock in the prophecies:

But tis
strange; 
And oftentimes, to win us to our harm, 
The instruments of darkness
tell us truths, 
Win us with honest trifles, to betray's
In deepest
consequence...

Macbeth clearly values his counsel,
because he asks that they might speak again about what they have witnessed after they have both
had time to think about it. 

By Act III, Scene 1, the murder ofand Macbeth's
accession to the throne have soured his relationship with Banquo. The scene begins with ain
which Banquo shows his fears that Macbeth is responsible for the murder of Duncan:

Thou hast it now: King, Cawdor, Glamis, all, 
As the weird
women promised, and I fear 
Thou play'dst most foully for't...

Banquo is somewhat encouraged, however, by the fact that Macbeth's
prophecy has come true, since the witches also predicted that his sons would be kings. Banquo
tells Macbeth that he is going riding with , and Macbeth asks a number of questions that could
cause the audience to (correctly) predict that Macbeth plans further foul play on Banquo's
riding excursion. Banquo has become an obstacle to Macbeth's ambition, and must be
eliminated.