The eyes don't lie , make eye contact when ye talk. You will know
You could ask him.
He will want to know you more and more. He will be eagerly waiting for your response to each of his message. And yup eyes just give it away.
He calls you, texts you, appreciates your poetry and photography when you yourself know they are not that great, plus he follows you around like a magnet.
I feel you can't... these things just happen and then you can look back and see it is. "If love is not madness, it is not love." - Pedro Calderón de la Barca
By asking him :)