Probably because Damon is a douche until you get to know him. He's got hidden depths.

Dean is glad he could help him figure it out? Seriously though, Dean is here to help Castiel figure out how to have a life, whether he's an angel or human. Cas's answer makes Dean's brow furrow. Now he's a little concerned. "Okay...well, if you want to stay an angel...we'll figure out a way to get that connection back somehow." Dean doesn't want Cas to go home either mostly because he's selfish and he does want a life here, a life that includes his best friend.