You'll be able to identify closely with this person's needs, and they will certainly recognize and understand yours at a deep, instinctive level. Their support, in fact, can help you to develop your core strengths as a person, because they understand you so well. You may not even need to verbalize your thoughts, needs or hopes for the future; this person will simply grasp where you're coming from, often without having to be told.
Continuing a relationship with this person will lead to important personal transformation, because their purpose in your life and their effect on you will be to help you become stronger, more self-aware and effective in your own life. Your shortcomings and insecurities will seem to melt away the longer you know them, and the more you talk with them about your feelings, desires and opinions, the more you will grow to understand yourself and trust yourself. This will be a mutual experience; you'll return these gifts to them as well as using them in your own life. And your emotional connection will enhance your sexual connection, which will be another facet of yourself that will become empowered through your relationship with this person.