What do you think of love?
They say it's shown in altruism, since we -human beings- are selfish. Do you think altruism exists? There are, indeed, times where we prioritise the needs of another, but do we really not get anything out of it?
We make mistakes, sometimes too much to the point where we doubt the welfare of our souls, and assurance would be needed; an act of humanism that proves all conclusions wrong and repaints us as pure-hearted angels with no evilness. Remember a time, where you were altruistic and lost something in order to help someone, how did that feel? Yes .. delightful. The pleasure we feel after being good is what pushes us to be good. If altruism made us feel bad, no poor would survive, no orphan would be adopted, and no "Humanism" would've existed in dictionaries.
Love is the highest stage of that pleasure, it is joy. The joy of moving for the same desire, towards one direction, asking similarly interesting questions and digging deep, not to find the same answers, but the hidden room for two, the one that can fit -widely- an ocean of thoughts and -merely- a pair of souls. Love is selfish; it makes us feel fulfilled, and so we search for it. It's when you're willing to satisfy the other's lack of happiness in order to feel good about yourself. Poetically selfish.