When Cas died in Chuck's house Dean felt... something... He wasn't entirely sure what it was and didn't particularly want to find out. So being the emotionally constipated man he is, he shoved whatever it was to the deepest darkest corners of his mind and left it there to rot and fester.

That is, of course, until he spent how ever long it was hunting down the Angel in Purgatory. Dean realised he was feeling love, and in no way was this platonic, for the Angel. He might go as far as to say he was in love with him. Which was a scary thought. Dean had no idea that Cas was trying to protect him by staying away in Purgatory, if Cas had told him that was the reason before he left, Dean would have punched him, however ineffectual, in the face for how stupid that was.

After Dean had escaped Purgatory with Benny he developed, what many would call, survivor's guilt. He felt guilty about getting out whilst Cas was still stuck in that place (he would describe it as a hell hole but in hell it wasn't a case of hunt and be hunted). Everyday Dean would feel some kind of tug. It was pulling him back to Purgatory, back to Cas. That was when he realised that this was more than love. It had to be. No amount of love would ever physically pull a person towards a place like Purgatory.

Sam and Benny were the only things keeping him from finding a way back, opening a door if he had to. He needed, no he wanted his Angel by his side.

Then Cas was suddenly back and Dean had no idea how to react. At first he was ecstatic, if a little shocked and was far too excited to say anything to him. But then, Dean noticed differences in the Angel's behaviour, for example when he killed that little angel dude... what was his name... Alfie?

Then in the crypt. Cas was beating him down. "Cas. Cas, I don't know what the hell is wrong with you, but if you're in there and you can hear me, you don't have to do this." He didn't understand why. Cas had no reason to kill Dean, but that was the impression that Dean got, the Angel was trying to kill him. "Cas!" Dean doesn't want to believe this is Cas, he can't. This can't really be Cas. Can it? He can't be in love with a being that wants to kill him. "Cas, fight this! This is not you! Fight it!"

When Cas let slip the name "Naomi" Dean definitely knew there was something wrong. Something he needed to fix. Cas was under some kind of mind control and he needed to break it. "Cas!" There was only one way Dean could think of to break this Naomi chick's control over Cas, and that was with an admission, a confession. "You want it?" He would try whatever he could to get his Angel, his Cas back. "Take it! But you're gonna have to kill me first. Come on, you coward. Do it. Do it!" Dean had to get Cas back and if it took his own death then he would go through with it.

"Cas... This isn't you. This isn't you."

"We're family. We need you. I-" He couldn't say it. Not then at least. Even if Cas weren't under mind control Dean wouldn't have been able to say it. It reminded him to much of Cassie and Lisa and every other failed relationship he'd ever had. "I need you."

Then suddenly, the control is broken, but Dean didn't know that. All he knows is that there had been a very bright glow and his was beaten and bleeding, barely able to shield himself from the brightness. Cas was free and he planned to right the wrong he had just committed by healing Dean.

Metatron caused a whole heap of problems, the angels falling, Cas being human, the angels being bigger dicks than usual, Cas getting laid, all the dead humans destined for heaven being trapped on Earth, Cas being killed, Gadreel sinking his angelic teeth into Sam's meet suit (Dean blamed himself for that one but he could blame Metatron too), Cas nearly getting a girlfriend, and many other non Cas related things (As well as several Cas related things...). But of course Metatron caused the biggest problem when he killed Dean.

Dean, having the Mark of Cain, never actually died. But for all intents and purposes, Dean was dead to the world (and I mean dead dead, as in no afterlife dead) until Crowley woke his Demonic ass up. But in those precious seconds before Dean became dead dead (or not as the case may be) he felt a surge inside himself and realised it was love, true love like the Disney Princess One True Love kind of love. For one brief moment Dean was very confused as to who this love was for. But then he realised;It was Cas. Cas was his, for want of a better word, soul mate. And now look what's happened! Metatron had to go and ruin that too!