Everyone breaks down. You can't go through something like changing species and not have a meltdown. The question is when. The stronger people hold out longer. Cas' life made him strong. But Dean still knew a break down was coming, so he had to be ready. In the meantime, he treated Cas just like everyone else.
It was a bit of a shock when a loud crashing noise woke Dean somewhere around 3:00 in the morning. He rushed to Cas' room where he found a bloody, sobbing ex-angel surrounded by a mess of broken... well everything. He was suddenly glad they were in the Batcave, not in some hotel where people could question the sound of things breaking.
Dean rushed over to Cas, ignoring the broken glass in his feet. He immediately wrapped his arms around Cas protectively. Cas leaned into Dean thoughts buzzing in his head. He was useless. He was fragile. He was limited. He just wasn't good enough. At least that's how Cas saw it.
After a long time, Cas' cries quieted and he relaxed into Dean. Dean could see he was just about to he was still shaken up, so he offered to move them out of the messed up bedroom into the living room. As they sat down on the couch Dean leaned forward.
"So, talk to me." Cas glanced at Dean before he lowered his head in shame. He was having a meltdown, something eh promised himself he wouldn't do. I just proved he was weak, worthless.
Dean gently held Cas' chin and brought him up to eye level.
"Cas. C'mon, we need to talk about this."
Cas sighed. "Dean I'm just not-"
"No. Don't you dare say you're not good enough, just because your a human now. You're a damn good hunter, you know way more than us about angels and Heavenly things. But you're also a good friend. You sacrificed so much for us, so why would we just leave you?"
Cas didn't have a good answer so he just stared into Dean's bright green eyes. He always thought those eyes were beautiful. They went along just perfectly with his freckles. Dean was strong, beautiful, kind. Cas needed him to help him up when he fell down. He needed him to keep going in life. He loved him.
Dean just stared into Cas' bright blue eyes and was lost in his own world. Cas underestimated himself, thinking the only goos thing about him was his Grace, when he was smart, innocent, adorable, string, and kind. Dean needed him to remind him that there was till good in this messed up world. He needed Cas to keep going. He loved him.
Dean realized they were faces were only inches away fro each other. He slowly started to close the gap, leaving Cas able to back out if he wanted. Dean finally reached Cas' lips and gave him a gentle, yet loving kiss. It was simple and amazing. Cas leaned into Dean, deepening the kiss.
When they finally came up for air, Dean said, "You still believe, your worthless?"
Cas shook his head and Dean said, "It's getting late and your room's a mess. Mine's big enough for two, though."
Cas broke out in a huge grin and followed Dean to his room. Little did they know, Sam had awoke when the crashes started, too, and saw the whole thing.