How do you know?

When those songs that used to make you cry now make you smile because you think about him.
When you can't wait to see that person again, even if it means leaving Hawaii.
When you think "This would be so much fun if he were here.."
When you you fall asleep and dream about him just talking to you and saying everything you want to hear.
When you watch and recount everything you say, just to make sure you don't say anything that would be even potentially stupid.
When any new text is cause for excitement.

That's how.