He was afraid to look at Ruby while he was working. What if he accidentally screwed his focus up and found her instead? The last thing that he ever wanted to do was make her a victim of what he was practicing. So when Ruby got close and started to kiss and talk to him, Sam gave it his all to keep his gaze on the demon ahead. He was screaming, but those sounds were slowly being tuned out at the words of comfort that Ruby offered him.
She believed in him. The demon screamed even louder as more blood leaked down Sam's face. Wincing, Sam closed his eyes at the 'I love you' and focused on nothing but pain. Not because he was angry any longer, but because Ruby needed to see that she wasn't making a mistake by believing in him. He was worth it. He wasn't a waste. She'd be proud to know that she was in love with him. He'd make sure of it.
His vision blurred slightly, the pain in his skull doubling, but Sam did not budge. It was only when the demon's head drooped forward and the screams muted themselves out did Sam let his arm drop to his side before falling to his knees onto the floor.
He needed a break. And that demon appeared to be unconscious. That'd be good for now.