Eros is the physical, sexual side of love. It is needing and desiring, and wanting the other person physically. The physical, sexual side of love called "Cupid" by the Romans.
Agape is the altruistic, giving, nondemanding side of love. It is an active concern for the life and growth of those whom we love. It is most clearly demonstrated by a parent's love for a child. Agape is an unconditional affirmation of another person. It is a Greek term for spiritual love.
Philos is the love found in deep and enduring friendships. It is also the kind of love described in the biblical injunction "Love thy neighbor as thyself." It is also the greek term for the love found in deep, enduring friendships; a general love of humanity.
To have a love that includes all three is to truly be 'in love.'