1, 2. Fickle, inconstant, capricious, vacillating describe persons or things that are not firm or steady in affection, behavior, opinion, or loyalty. Fickle implies an underlying perversity as a cause for the lack of stability: the fickle seasons, disappointing as often as they delight; once lionized, now rejected by a fickle public. Inconstant suggests an innate disposition to change: an inconstant lover, flitting from affair to affair. Capricious implies unpredictable changeability arising from sudden whim: a capricious administration constantly and inexplicably changing its signals; a capricious and astounding reversal of position. Vacillating means changeable due to lack of resolution or firmness: an indecisive, vacillating leader, apparently incapable of a sustained course of action.

Did you mean feckless?