Kent's Confusion

"A brother? No, a butcher of thy friends.
Proud Edward, dost thou banish me thy presence?
But I'll to France, and cheer the wronged queen,
And certify what Edward's looseness is.
Unnatural king, to slaughter noblemen
And cherish flatterers! Mortimer, I stay
Thy sweet escape. Stand gracious, gloomy night,
To his device!"
(IV.i.4-11)

This act opens with Kent's declaration of his disappointment with King Edward, his brother, and his decision to side with the Queen and Mortimer, Edward's rivals. This is strange since Edward is his brother and he seemed to show his support for him at least somewhat through the beginning of the play. However, since no one in the play has been truly loyal thus far, it is not surprising that Kent would also be one to flip-flop, regardless of his relation to Edward. The surprising bit comes in scene IV (lines 1-18) when, in a monologue, Kent reveals his shame for having sided with his brother's opposition and recognizes how "unnatural" this is. He also finally reveals what, until this point, has only been suggested -- Isabella and Mortimer's affair. Kent's sudden "betrayal" is not completely without reason, however, since throughout the remainder of the act he frequently states the need to do away with flatterers and act in the interest of the state (England). This indicates that the only reason Kent has decided to turn against his brother is to protect the monarchy and England. I wonder if this means that Kent is the only level-headed character in this play, acting not merely out of spite like the other characters, but for what he believes to be best (especially since he is obviously hurt by his decision to turn against his brother) -- or if he is doing this in benefit of himself, which may be revealed at the end of the play. Although it is possible that Kent is the only self-less character (to some extent at least), it is difficult to not be wary of any of the characters in this play since they have all proven to be deceitful traitors at some point.