It is realizing that we are capable of loving more than one other person at the same time. Maintain openness and honesty.
Reassurance is essential during rough moments.
Hold as important the needs and desires of those you love and those they love as well. Compersion, being delighted with the joy that those we love find in relationship with others, is delightful when it happens - at the very least, be supportive of each others other relationships. Have community around who share or at least accept and understand one's polyness. Beauty, if it becomes vanity. Love, if it becomes possessive.