Dopamine and serotonin are commonly known as hormones that make you happy and are sometimes called "love drugs" but this "love drug", oxytocin, is something else. It plays a roles in maternal behaviors, anxiety, social recognition, pair bonding and orgasms and has also been rumored to be linked to autism: this article describes how a deficit in oxytocin could cause those with autism to have a lack of social recognition. Oxytocin also increases the levels of trust between people (see here), which could be why it is called a "love drug", and what is love without trust?
"Love looks not with the eyes, but with the mind"
-Shakespeare, A Midsummer Night's Dream, Act I, Scene I, Line 234