Meditation for Dummies by Stephan Bodian in Chapter 10 ("Opening Your Heart: Love, Compassion, and Forgiveness") explores four "cornerstones of a happy and fulfilling life" which he suggests are four dimensions of love:
Lovingkindness: Arises spontaneously in response to the kindness of others and consists of warm, loving, caring feelings that can be deliberately increased and extended.
Compassion: Takes love a step further. In addition to caring about others, you also feel their suffering and naturally feel motivated to help relieve it. (The word "compassion" means "to suffer with.")
Sympathetic joy: Is the flip side of compassion. It consists of happy feelings that arise in response to the happiness and good fortune of others.
Equanimity: Can be cultivated through the basic meditation practices taught in this book; also known as steadiness of heart. No matter what happens, you expand to include it without allowing it to upset or disturb you.