how do you know when you've fallen in love with someone?

Everything on your body hurts when they aren’t around. You don’t know what to do with your hands when they are around. When you hear their voice, everything suddenly starts to make sense. Almost as if you knew the answer, but you had to wait until they said it for you to understand. Their skin against your skin isn’t two different textures; you mix together properly. I think when you fall in love, you just.. know. Like how you know you’ve had enough. You.. you just know.