"Trying is all I can ever ask," Castiel pointed out. To ask someone to succeed all the time was an unfair burden to put on anyone, human, demon or even angel.
"Believe me, I am well aware of the fact you're going to screw up sometimes," he half smiled as he held her. He knew there would be times when she would falter, just as he knew she was speaking with Sam Winchester again. He could see it all, and he understood why she felt the need to, even if sometimes it stung to see. Being an angel didn't mean he could never feel the darker emotions such as jealousy and there was more than one occasion where he had had to resist the urge to punch the younger Winchester brother in the face.
"And I'm still going to be here," he continued, as if his thoughts had not even wandered a little bit. "I'll be here if you screw up, I'll be here if my family come back and try to make everything a mess again. It doesn't matter, I'm not going anywhere."