You can stay in a relationship because of social responsibility even when there is no love. But to stay in love, you have to be in love. If love has once invaded, it never leaves. It only grows with commitment, duties etc.. Romance works like oxygen to keep the love refreshing. I do not think that love ever fades away. It only changes it's form of expression or romance with the age of relationship and with the two people in love growing together. If it has faded away then it was not there. In that case we have misunderstood infatuation, expectation and commitment as love. Love is purely about acceptance and giving space. It is true for all relationships.