Question: how do you know when its love? 

Answer: When you realize that it's more than just having someone to cling too.  Or someone to have sex with.  You know, when you hurt when they hurt.  You are happy when they are happy.  They are your partner on a mental, physical, and spiritual level.  And you know that you would sacrifice everything you have for them without thinking about it.  That's when you know it's love.
This question from the Yahoo Q&A forum is categorized in the topic: Sports