Dean wasn't entirely sure when these new feelings had surfaced. If he was honest with himself then they'd probably first started when Castiel had spoken to him in the park after they had lost the battle of the seal with Samhain.
The unfortunate addition of Uriel to the party had not helped Dean's spirit, while he sat on a bench in some 'unimportant' town with an angel, but he had felt a certain sense of satisfaction that he'd essentially told the smug little shit just where he could go.
The elder Winchester remembers the moment quite clearly. Cas had just opened up to him about his impeding doubts and Dean felt a certain empathy with this warrior of God he hadn't previously. To be honest the angel had alarmed him slightly because for the first time in his life he had no idea how he would defend himself if Heaven suddenly turned against them.
Castiel had turned to look directly at him and the sun had caught his eyes at just the right moment making them appear as cerulean flames in the dusk and Dean found himself startled by the wave of lust that shot through him. The angel or at least his vessel was undeniably gorgeous. Now what the hell was he supposed to do with that knowledge exactly?
Of course being Dean Winchester this meant that nothing was ever easy and he spent the next several days panicking that he might be gay and that he hadn't even realised. In the end he decided it didn't matter it was just some trick of the sunlight, he wasn't really attracted to Cas but he'd objectively noticed his eyes were pretty, which anyone would have confirmed.
Sam of course noticed nothing.
So he put it out of his mind, but the next several times that he saw the angel he couldn't help but glance at his eyes, then the curling dark hair, the slim physique, until finally he admitted defeat and agreed with his traitorous body that he was indeed attracted to his new ally. At least in a physical sense. Physical stuff Dean could deal with but then he started to find himself becoming irrevocably fond of Cas in general.
The social naiveté made Dean just want to lock him up and keep him safe from the world before he remembered that the angel was a formidable warrior who could kick serious demon butt. They had formed a sort of friendship which made his ever growing feelings adapt to something more important than lust. Something he wasn't quite ready to confront. Then Anna came into the picture and suddenly things weren't quite so clear.
He just couldn't believe that Castiel would harm an innocent girl like that and even when the truth was discovered he still couldn't understand. He slept with Anna but some increasingly loud voice (his conscience perhaps?) was screaming at him that he only did it so he could settle for having any angel even if it wasn't the one he wanted.
Dean did understand eventually, when the angels and demons confronted them in the barn, Cas's sorrowful look, he didn't want to do it. He was just being a good little soldier for daddy and Dean got this overwhelming sense of déjà vu that was him just a few years ago. Obeying without question, more weapon than son.
He met Cas's gaze when he stopped Alistair from exorcising him, and Dean could have sworn that something passed between them in that split second. A current of some kind, electric and intoxicating.
The next time he saw Cas was one he'd rather not remember. Torturing Alistair was not something he wanted to do but honestly that Uriel turned out to be the traitor wasn't that surprising in the end. On the other hand he really didn't want to know that all this was his fault. He hated Cas right at that moment
After that was the whole weird other life experience in which the brothers met Zachariah, another angel he didn't particularly like, then again he wasn't too pleased with the other one at the moment. He'd told himself to forget any misguided feelings he might have had towards the blue eyed creature and that it was just a passing attraction to a vessel.
Then Cas appeared to him in a dream and asked for him to find him because he had something to tell him, and the minute he laid eyes on the angel all those annoying feelings came rushing back. Him and Sam travelled to a warehouse that looked like a bombsite and instead of Cas they found Jimmy Novak.
Dean wasn't attracted to Jimmy at all. In fact he found him slightly irritating, mostly because he reminded him of Cas but he wasn't. Whilst still attractive, Dean was eventually forced to admit that without the angel the vessel did nothing for him. This whilst startling lead to a more pressing realisation.
He was in love with an angel of the Lord. Also his brother had apparently turned into a demon blood drinker. Shit.
It all came to a head in the mysterious limbo like room Zach had dropped him in to 'keep him safe'. Bollocks. He was in here while Sam headed to fight Lilith. No freaking way.
He bartered and argued and maybe even begged a little but Zach wouldn't budge. Then Castiel showed up and Dean desperately tried to get him to see sense, to help, anything. His frustration rose and he called the angel several names and Cas just stood there blinking at him with those adorable baby blue eyes and casually mussed hair and Dean did the only thing left that he could think of.
He kissed him.
He simply grabbed the angel by the edges of his seemingly indomitable trench coat and pressed their lips together. Cas quite understandably froze in shock throughout this event as his charge pressed him up against the nearest wall and took exactly what he wanted. Keeping their lips connected and running fingers through his hair before releasing him and taking a step back.
They stood there the angel and the human, flushed and panting, staring at each other for what seemed like forever before Cas quite unexpectedly disappeared.
A/N How much do you hate me for the cliff-hanger? This is going to be a three shot and if you can't already tell by the rating there will be smut. Probably in chapter 3. Hope you like.