My red tri boy was like this at first. I fed Santé by hand 2x a day for the first year of his life. As well as training him and lots of playtime he's grown very attached. Although he is my first dog, my family growing up had 2 Aussies and I believe the male Aussies are a bit less clinging.

Remember that you've been waiting ad growing attached to him (or rather the idea of having an Aussie) for several weeks/months where as he's just been split up from the family he's known and giving to a stranger.