what is love?

I was listening to a song by NeverShoutNever (http://www.youtube.com/watch?v=KA62IuYI6gs) and it made me think, What is Love?
To me, love is when you think you might never see a person again and it makes you cry. Its when that person is on your mind every moment of the day. And even if you know you cant have them, you want them more.

Here's some answers I've gotten from some of my friends:

"Love is when you can trust someone completely to be there for you... no matter the circumstances... someone who you know will have your back through thick and thin..someone you would die without."
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"When you want to spend forever with someone."
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"To me its when you have this tender and passionate affection for someone.When you see someone and you can't help but smile. Like when I see the person I love I get all nervous and like blank out and my heart just melts that's when you in love."
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"Love is something that you feel with the person you feel like you can be your self around."
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"Love means to me: When u really get butterflies talking to that special person and you cant get them out of your mind and all you wanna do is be with them and you can talk about anything with them and not hide anything."
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"I think love is giving your heart to the person which you love and you will be willing to do everything you can for that person."
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What do you think love is?