If you vacillate between two alternatives or choices, you keep changing your mind.
例句
She vacillates between men twice her age and men younger than she...她犹豫不决,不知道是该选择年龄比她大一倍的男人还是比她小的男人。We cannot vacillate on the question of the party's leadership.在党的领导权问题上我们不能动摇。
英汉词典释义
vi.
犹豫; 踌躇; 游移不定
Such parents vacillate between saying no and giving in—but neither response seems satisfactory to them.这类家长举棋不定,对孩子们的无理要求,不知道是该回绝还是该满足,觉得这两者都不理想。
英英词典释义
Verb
1. be undecided about something; waver between conflicting positions or courses of action;
"He oscillates between accepting the new position and retirement"
2. move or sway in a rising and falling or wavelike pattern;