How do you know what you are feeling is truly love?

When you have reached the point in which Idealism replaces reason.
you would behave in an impractical and idealistic manner, knowing fully well it will hurt you in the long run. Almost like you have lost your common sense.
When you literally start to do stupid things.
When you think about that person, everyday, first thing when you wake up and last thing before you slee . They consume your everything thought. And you relish every thought and fantasy you have of them.
When you would be with that person no matter the circumstances, even at the worst and most abject of all situations and not think twice about it. It doesn't matter if everything goes wrong, because there's that one person, that makes it seem right.

If you haven't reached this point yet, then you don't know the meaning of love, thus the phrase "i love you" would be used in vain, and just be a cliched and meaningless thing to say. If you have reached this point...well, I hope it works out for you. Because being in love is the most insecure feeling in the world, especially if the other person doesn't feel the same way.

My way of describing love is the feeling of your pounding heart, the way that you can't seem to stop thinking about the person when they're not beside you and that you want to spend every single spare time of yours to be with them. You feel like you can't live without them... all your troubles in your life are gone when that special someone is in your life, it feels like all your problems have gone away. You can't sleep at night cause you think about them so much... and no, love is not about having sex... I believe people can love one another without having sex until they're married, now that is TRUE love, and not just lust. That's my opinion anyways.

Love is very complex, especially given the varying types and degrees one can have.

True love is probably the hardest thing to define because it is so much more than just one thing. It's happiness when you're with the person (I'm speaking generally since fights happen), it's thinking about the person all the time, it's having strange little random things remind you of the person, it's feeling like you want to be with the person all the time, it's caring for the person and know you are cared for back, it's being able to be with this person through the good and the bad, it's a sick feeling in your stomach when you're around the person that doesn't feel bad but you can't explain, it's a desire to be with that person more than others, it's chaos and simplicity at the same time, it's missing the person when he or she is gone, it's wanting to call the person right back even after just hanging out, and more.

Sometimes love will creep up on you slowly and other times it's like WHAM! to the back of your head with a frying pan.

It's different for everyone, and yet it is the same as well.

You'll know it when you have it but you may not recognize it at first.

Confused? That's alright, I think that's the point.

Love is feeling like you are going to die if the person you love is not in your life! Actually aching when you think of her, and she's not around! Thats love to me!

Let me define love:

Love is a feeling shaped by social regulation of sex, marriage, family, and gender which has redefined itself throughout history.

Love is the substance vital to keeping marriages together as every culture has their own system of marriage rules. So in our culture, think about what keeps our marriages together?

In Hunting and gathering societies, marriage is simply providing. So their practice of love is a man who can bring home the goods while the women prepare it. That's their love.

Ours however, is a little more complex so you'll have to decipher that yourself. What keeps us together is love. Everything else is perks and lusts.