Love is much more than simple 'a sum of chemical reactions in the brain''.
You are not just your physical body but also your spirit, your spiritual body.
Your physical body needs food in order to survive and to grow but your spiritual body needs love in order to survive and to grow.
So, your spiritual self (connected with God) pushing you to share your hearth and love with others.
If you don't follow your spiritual self, you die spiritually.
We can see love in so many forms and ways around the world, so we can't deny it.