fickle

英['fɪk(ə)l] 美['fɪkl]

1. marked by erratic changeableness in affections or attachments;: "fickle friends"; "a flirt's volatile affections"

2. liable to sudden unpredictable change;: "erratic behavior"; "fickle weather"; "mercurial twists of temperament"; "a quicksilver character, cool and willful at one moment, utterly fragile the next"