Cas didn't understand the appeal of humans' concept of intimacy.
He'd had sex exactly twice during his time among humans.
The first time was shortly after Megatron took his grace.
He'd been taken in by a young woman.
She had ended up being interested in Cas, and it seemed common for the relationship between a male and female to develop to that level.
He hadn't found the the deed unenjoyable, per se, but he had definitely not found it pleasurable.
Luckily, he had become somewhat apt at pretending, lying, acting. He was glad to have left the woman free of any guilt he could have caused.
Cas wasn't certain about the significance that came with his inability to recall the woman's name...
Cas often thought back on this, the lack of pleasure that he was supposed to have felt.
So, at the end of the year, with Dean missing and Sam looking for him, he decided to try something before going to put heaven back together.
He used his observations of Dean in order to find, what humans called, a 'one night stand'. Cas managed to 'pick up' a man, and they went to his motel room.
Cas wasn't sure how to describe the experience, other than better than the first one.
All of this was before Cas realized something so obvious to everyone around him.
Something that was right in front of him.
Something he had actually known for years.
"Dean," Cas softly greets, his eyes instantly drawn to the green-eyed man. "You wanted to see me."
Shyly, Dean smiles at him.
"Yeah." he whispers.
As he gets closer, Cas fights every part of himself that wants to step back, step away. When Dean stops, Cas can feel his breath on his face.
"I could've never seen you again, Cas," Dean quietly says, but it feels loud in such close proximity. "But I wanted to. That's why I'm here. You're the reason I'm still here, Cas. I love you."
Sharply, Cas inhales.
"I know," he tells Dean, gazing into his grass green eyes. "I love you too."
When Cas notices Dean still smiling, he smiles himself.
As Dean leans closer, Cas breathes in and closes his eyes, not knowing how this would turn out with Dean doing it.
Their lips touched, softly.
When Dean starts moving his mouth against Cas', Cas sighs. Gently, Dean holds Cas' waist and Cas holds the tops of his arms.
This is good. So far.
Suddenly, Dean is tugging at the wonky tie around Cas' neck. When it falls to the floor, Dean pulls away slightly, with a grin.
"Come on." he eagerly encourages, pulling Cas' hand.
Cas never could say no to Dean Winchester.
Cas feels Dean roll over next to him.
"That was good, huh?" he murmurs beside Cas' ear, a hand on the angel's bare chest.
Cas merely hums in agreement, as though he's distracted or deep in thought.
"Cas?" Dean asks, frowning and propping himself up on his elbow. "You did enjoy that, didn't you?"
Cas freezes, suddenly feeling very afraid.
"Yes?" he replies, uncertainly, his answer more of a question.
"No, you didn't," Dean breathes, sitting up properly. "You should've told me! What was bad about it?"
"Nothing, as far as I could tell." Cas assures Dean.
"Then what was wrong?" Dean desperately demands. "Is it me?"
"No!" Cas exclaims, bolting upright. "No! Of course it's not you, Dean. I am certain it's me."
"What do you mean?" Dean A's, being careful not to cross a line.
Sighing, Cas closes his eyes and shakes his head.
"Each of the three times I have had sex, I have not found it as enjoyable as is always promised," he begins to try to explain. "It's not that the experiences were entirely unenjoyable, though, which confuses me. However, I have never done it out of my own interest or because of my wants. The first was because of the woman's interest. The second was an experiment to see if I found intimacy with a man more pleasurable. The third because... The third time was because I can't say no to you, Dean Winchester."
With a small smile tugging at the side of his mouth, Cas looks up at Dean.
But Dean just frowns at him.
Fearing that he's ruined any chance at a relationship with Dean, Cas sits up, not making eye contact with the man next to him.
"I... I think I should go." he quietly says, moving to get off the bed.
"Wait. Cas," Dean interrupts, gripping Cas' arm. "If... if you want to try this... this relationship between us, I'm on-board. But we don't have sex unless you want it. It was good, but not that good."
When he glances at Dean's nervous, teasing smile, Cas finds a smile of his own curling onto his lips.
"I would like that. To try that," he tells the hunter. "But... I'd like to get dressed before talking about it."
Dean smiles charmingly, before leaning back.
"Sure thing," he calls. "I'll still be here."
And he is.
And he will stay there for a long time after, as well.