Breaking down the house

We are now in the process of listing and selling our condo so that we can move to a bigger place in Bridgeport; this involves stripping all the personality and life out of our current abode. At first I was a bit sad about depersonalizing our space, but after I thought about all the good that would come from being able to sprawl out, those feelings passed. Dan, on the other hand, seems to be a bit more melancholy about the whole thing; when it comes down to it, he does want to move, but he's a bit sentimental about leaving our first home together. I wonder why this isn't affecting me in the same way. I guess I went through all of these emotions when we left the first place we lived together (but didn't own), which was also my grandparents' former home, and the setting of many of my most fond childhood memories.

What I am wondering is, why do we get so blue when we have to move on from a place that was happy and positive? Shouldn't we be able to leave with the fond memories we have created, especially under circumstances where we know we are making a change for the better? As time goes on, those old haunts become legendary in our minds; places where nothing but good ever happened, and everything was perfect - a moment in time you'd love to return to because you forgotten all the downsides, like thinking of an ex-boyfriend or being in High School. Thankfully, we can only go forward from here.