inconstant
adjective literary uk/ɪnˈkɒn.stənt/ us/ɪnˈkɑːn.stənt/
（尤指在感情、行为或择偶方面）多变的，不忠实的，不专一的
not staying the same, especially in emotion, behaviour, or choice of sexual partner
an inconstant lover 用情不专者
Opposites: changeless constant incessantinvariant never-endingperpetual