"The agony of loving someone who does not return my love is killing me." Luther thought as he pounded his chest while looking straight at the person he loved.
What is this horrible truth? Mila doesn't love him back.
Being aware of this is a lot of pain, and he doesn't want to let go. He even questions why she doesn't love him at all or why she won't even try.
He kept expecting and thinking that she would come to adore him, eventually.
Because loving someone who does not reciprocate your feelings sucks, and "someday" is in the future, while he is in the present.
What's the point of enduring agony in the hope that things may improve in the future over which you have no control? What if it doesn't happen?
The best thing to do is to accept the truth, no matter how painful it may be. However, it is not what Luther wanted to do.
"Why do you always worry about him?" he exclaimed indignantly.