to play就是：玩，fast就是：快，loose用在这里，它的意思就是：轻率的，不在意的。要是说一个人play fast and loose，那这个人就是不负责任的，靠不住的，反复无常。

【例句】
He had been allowed to play fast and loose long enough.
大家容忍他反复无常地玩弄手腕够久啦。

I feel sorry for Mary. Jim has been playing fast and loose with her affections too long. Why doesn't she make up her mind once and for all, and just get rid of the man?
我真是替玛丽感到难受，因为吉姆长期来对她的感情毫不在意。她干嘛不干脆下定决心和他分手算了？