When you love someone, you can just read what your lover thinks about. Most of the time, you share the same ideas with your lover. You can easily understand him or her. You can tell what your lover thinks about or wants to say without waiting for him or her to say anything. Thus, it's sharing the mind.
Love makes lovers love the same things.
If one person loves one kind of music, the other will do the same. They always like to love same things because they love each other. Thus, it's sharing the heart. Sharing the spirit is the most wonderful thing about love. When two people love each other they feel the same all the time.