Intimacy, communication, and committment. By being intimate, you are comfortable around the other person. Communication creates fewer fights, better choices, realizations, and a stronger relationship. Committment helps make a stronger bond, makes longer relationships, and adds to security.
Love is not needed in starting in a relationship. As the relationship continues, the couple will learn to respect each other and learn to love over a number of years. Arranged marriages have this happen all the time.