The relationship between reason and emotion is complex, multi-faceted, and not yet completely understood. Most philosophers and social scientists consider emotion to be pre-rational; that is, we experience emotion before engaging in rational thought processes. For example, if you see a lion running toward you, you experience fear before you rationally calculate that the lion means you harm. Due to the pre-rational nature of the experience of emotion, we often depend on emotion to make split-second (or "intuitive") decisions.
On the other hand, reason can change emotion. You may feel sad because you have to move far from home. After thinking about the benefits of your move, that sadness may be replaced with a sense of excitement or happiness. The relationship between reason and emotion is thus not uni-directional, rather, each influences the other.