What is love? (baby don't hurt me)

Obviously "love" exists, even though it's intangible and everyone has different definitions of what that word means for them. There's a biochemical aspect of it as well. But what do you think the evolutionary reason for it is?

For example, pain only exists in our head as a way to tell ourselves that we are in danger and our survival is potentially at risk. Not every species has that. (central nervous system)

So, what's the purpose of love?