not constant; changeable; fickle; variable: an inconstant friend.

Is inconstant a real word?

not constant; changeable; fickle; variable: an inconstant friend.

What does it mean to be inconstant?

inconstant, fickle, capricious, mercurial, unstable mean lacking firmness or steadiness (as in purpose or devotion). inconstant implies an incapacity for steadiness and an inherent tendency to change.