I applaud Andrew Dabb because that episode perfectly and I mean PERFECTLY portrayed Cas as the beautiful character that he is.
So to quickly recap:
•At the start of the episode we see him standing outside the motel room, obviously having rushed back after realising something was wrong.
•He then feels guilty about what has happened and takes a verbal beating from Mary, accepting the blame for the whole thing. (We know that Cas has not been in a good place mentally in recent episodes so nicely incorporated).
•He then seeks help from Crowley, determined not to give up.
•After this, Cas, when prompted, is able to reel off the exact number of months, days, and hours since his best friends went missing.
•We then have a gorgeous heart to heart between Cas and Mary where he admits to trying to hunt down a vampire and failing. This scene is extremely powerful and truly gives us an insight into just how much Cas has tried to pick up from the Winchesters over the years. We’ve seen in previous episodes this season that Cas is capable of hunting solo (so be it Crowley was there too but it still counts) but this episode proves that he clearly does not cope well he knows there’s no one there to help him if he needs them. In any other episode, if Sam and Dean were just a phone call away, Cas would have tracked and killed that vamp in no time at all. But fast forward to this episode and Cas, in the mental state we observe him in this episode (and more broadly this season), clearly was unable to switch off all the shit going on in his head, and he very very clearly blames himself for that. He sees those dead girls as being his fault, just as he sees the Winchesters being taken as his fault too.
•And then at the end of this episode we get the speech. And forgetting even the contents of this speech, the way it is delivered by Cas is just heartbreaking. He is incredibly close to tears, he’s struggling to even maintain eye contact with the Winchesters as he says it, and his voice wobbles and breaks at points. Cas will believe that he was selfish for killing Billie, because he killed her so that he wouldn’t lose his best friends, and so that his best friends wouldn’t lose their Mom once again. By the end of this episode, Cas is willing to trigger something unknown because he loves those guys so much that it scares him to consider them gone forever. He knows now, after the months apart, the failed hunt, and his own mental disintegration that he NEEDS them. Because after witnessing just how not in a good place Cas is right now, he is clinging to them and just praying that they don’t get tired of him and shove him away. He is showing clear signs of depression, and being separated from the brothers only made that worse. And all of the above came together in one big heap of sadness, guilt, loneliness, and depression which resulted in that speech. A truly amazing character development for Cas.