Derek knew that he had crossed a line which he wasn't quite sure he could recover from. He hadn't meant for it to get as out of hand as it did. She had barely looked at him since the moment they had left the apartment. Seemingly she was fine, addressed him in conversation, she put up a great front, but he saw right through her. He saw how hurt she was, and angry she was at him for being such a dousch bag.

"What'd you do?" Aaron asked discreetly as he and Derek went to the car to pick up more gear for the picnic that they had packed. Derek sighed and gave Hotch a brief account of that mornings exchanged.
"Out of no where she just got mad at me."
"Out of no where. Derek, when did you ever know Penelope NOT to challenge you to be a better person? Of course it worries her when you act so carelessly. You can't tell me that you wouldn't be reacting the same way had you found her in the same state of mind."
"I know. I miss you guys. But there's barely any time to eat or sleep let along make life long friends. Besides, this isn't permanent. I'd said I'd give it a year, but I am coming home Hotch."
"Are you sure that's what you want Derek, that you're making your decisions for all the right reasons? You're doing a great job in New York, they couldn't be singing you higher praises."
""Hotch, I get that. I know I've always had career aspirations, but now that I am in the middle of it, I think, at what cost? I am miserable in New York, and all I do is work. Surely there is more to life. Heck I know there is. I don't want a job that has me so busy I don't even know what's going on in my family's life, and that's where I am heading, and I think a part of me is already there. The job is fulfilling, don't get me wrong, but it's not enough for me Hotch. When this is all over, I want to come home. I will come home."
"As long as you're sure."
"More than sure." He said looking at Penelope playing with Jack with longing in his eyes. Hotch nodded in understanding.

"Did you two have an argument?" Emily asked point blank. Though Penelope had convincingly upheld the pretense that all was well, Derek was not as good. She had caught Derek looking at Penelope apologetically, pleadingly, and longingly.
"No, not really." Penelope paused and considered deflecting but saw the determination in Emily's face, like a dog with a bone.
"He just irked me this morning. It wasn't anything big, but it blew up into this big thing. Words were said, and I don't know Em." Penelope filled in the blanks for her friend as they walked towards the lake leaving the rest of their crew doing their own thing.
"He misses you P."
"I know that. I miss him too. But you should have heard him Em, he snapped. He basically blamed me for where we are. That he went to New York at all. Like I shipped him off to New York without a care in the world."
"He's scared."
"Of what?"
"Of Gabe taking his place as most important in your life."
"Are you kidding. Gabe is great, but I'm just getting to know him. Derek and I have been friends for almost a decade." Penelope protested.
"Yeah, but Derek isn't here to be a part of your decisions, or to see your interactions, to know that you miss him as much as you do."
"He's an idiot if he doesn't know that I miss him. Gah! He makes me so mad."