You will find no hate on my blog. I enjoy Supernatural and the many characters. Maybe I just see things a little differently. Besides, Dean has left Castiel before in the mental hospital to be watched over by a Demon. I feel Dean has obligations and when he feels he’s met…
Dean worries about Cas because he cares about him, not (or not solely) out of a sense of obligation.
"I don't need to feel like hell for failing you. For failing you like I've failed every other god forsaken thing I've ever cared about."
That sounds an awful lot like when Sam was killed in season 2 and Dean monologued about letting down the people he loves. Not only does Dean care about Cas, Cas is in the same category for him as his father and Sam. And I don't really think that's up for interpretation at this point, since Dean stated that pretty near explicitly.
As for leaving Cas in the mental ward, what else were they supposed to do? Cas was catatonic and Sam and Dean were entirely unable to care for him.