Love is valuing the joy and pain of another being like we value our own. We instinctively seek our own happiness and take action to relieve our own discomfort; love makes us instinctively do the same for others.
Love is not merely service (action) nor is it merely delight in the beloved (infatuation), though it can express itself in both of these. Loving someone means being able to choose what is best for them over what is best for us. Desire and possessiveness are false love because in both the focus is on us--our needs and wants. Sometimes love means letting go.
Love makes life rich by making us part of something bigger than ourselves.