Sam knew that they'd be able to help, possibly faster than if he worked on his own, but the way Sam saw it they could do their part to help without him being around. He wanted Dean back more than anything, and he felt he could help more if he was constantly on the move. Plus he couldn't take sitting around with the Sterling sisters with them sneaking pitying glances at him.
No, there were reasons Dean'd told him he was just like his father, and being a loner in times of grief was one of them.
"Alright. I'll come." Sam finally conceded, slipping a hand into his pocket to check for the Impala's keys. They were in there, and luckily for Sam he hadn't been one for unpacking lately--all of his stuff was in the car. "I just have to use the bathroom first."
Sam didn't wait for permission before he walked into the bathroom and locked the door behind him. He waited a few minutes before he flushed the toilet and turned on the water. The added noise sounded like it belonged and masked the sound of him sliding open and then shimmying out of the window.
It'd been pretty obvious that Deena wasn't going to leave, and that clearly meant that Sam had to be the one to make his exit. Within seconds he was in the Impala and starting it up. "I promise, Dean, you'll be driving this soon."