How can you tell when someone truely loves you?

I am inlove with this guy and he says he loves me too but i wonder sometimes. He uses the words but doesn't really show it, like i hope he should. The thing is i believe him when he says it but then something happens and I begin to second guess myself. Sometimes he makes me feel like i am always at wrong for one reason or another, i would try talking to him but he just shots me out. Could it be because he is insecure or could it because he wants out but can't make up his mind? i love him and it hurts..... so bad.... how do i know when to walk away and when to stay?