In the first line, he is saying to his lover not to stand up and leave him even do that this day could be any day! He is imploring her to stay with him. In the second line he says that she is so beautiful that from her eyes the light shines and he is saying that if she leaves his heart will stop because he cannot live without her. He knows that she has to leave which makes him emphasise that despite the fact that they must part, he does not want that this love to end because his reason for being happy will leave and die without the possibility of growing a little more.