Love, or charity, is: a divinely infused habit, inclining the human will to cherish God for his own sake above all things, and man for the sake of God.
Pretty simple, eh? A divinely infused habit, meaning, God makes it possible to practice love, and the working of that habit is manifested in the cherishing of God because he is infinitely worthy of love.
Only God can love God adequately, because only a perfect lover can perfectly love a perfect beloved. We should do our best, loving God with all that we are and have.
And man loves man for God's sake, because of what we see of God in man, because God has commanded us to love each other, because of God's example, because to love God's most cherished creation is to love God himself.
The emotions get involved because we are emotional beings, but the primary element in love is in the will. Which is good, because sometimes we can will something good for a beloved, but be unable to actualize it. As in St Therese's case, wanted to bring God to all men as a missionary, her desire had to take the place of actually going out and proclaiming God's goodness and mercy as a missionary.
Little children, let us love on another.
The failure of Christians to love is the greatest cause of the world being unconverted to Christ. I, of course, am first among these who fail.