Ideally, friendships lead us into deeper communion with each other; those we love mirror the divine reality and so draw us closer to the One they reflect. In our humanness, however, we can forget that the friend is only a reflection of God and instead invest ultimate meaning in the relationship.
Peace of mind has nothing to do with the external world; it has only to do with our connection with God. Love really is the answer. We're here only to teach love. When we're doing that, our souls are singing and dancing. When we remind ourselves that we are spiritual beings, that life and love are the flame eternal, that's when our soul is nourished.