The Greek language has several words that all point to the general term "love". Eros is erotic love. This love is based a lot on sensation and desire. Such love drives those experiencing it to briefly become as one. Dating couples are a good example of Eros. Eros is sort of a selfish love: it depends on how much the self can benefit. If the relationship is no longer beneficial to one person or the other, it is not to last. Eros isn't perfect on its own.
Then there's Philos: the love of fondness. Philos is about give and take. Both parties benefit mutually by the relationship. Philos is seen in close friendships, family members, and other such people. Camaraderie is a good comparison. Philos could be considered brotherly love. It's based in respect and trust. Philos can be broken, however. If either person does not contribute, or if trust is betrayed, the love is fractured. Philos is also an imperfect love, but one that even non-romantic people should be familiar with.
Finally comes Agape. Agape is perfect love, and can only REALLY be seen in two places: The ideal marriage, and the love from God to creation. (Forecasting some negative response here, but bear with.) Agape is a love of sacrifice, patience, and forgiveness. Agape goes beyond the other two forms of love because it is selfless. The Bible says, "Love is patient, love is kind. It does not envy, it does not boast, it is not proud. It does not dishonor others, it is not self-seeking, it is not easily angered, it keeps no record of wrongs. Love does not delight in evil but rejoices with the truth. It always protects, always trusts, always hopes, always perseveres." (1 Corinthians 13:4-7) This is the love God shows for us, even if we don't recognize it. Marriage is supposed to be a reflection of the man-God relationship. Where a person unites himself to God in spirit, a married couple unite in flesh. Eros and Philos result in some kind of synergy that hopefully results in Agape. The ideal situation is that the two loves are healthy and mutual enough that both people involved take on an attitude of sacrifice, patience, and forgiveness.