Jealousy, emotional manipulation, possessiveness and control could become major components of this friendship if you're not both careful. Although dominating you will never bring them real satisfaction, your friend will try it anyway, because their connection with you will feel so important to them. Similarly, your need for true friendship could keep you locked into this pattern for quite some time, unless you can find a way to examine your feelings and needs and figure out why you've made the choices you have.
It could be that you feel an overwhelming need for companionship, and that will lead you into this controlling, emotionally complex situation. You'll both have to examine your emotional and relationship needs if you are going to maintain the positive parts of your connection.