I missed a girl once so very much too, I remember, at the end of the relationship. Its funny how things you took for granted become so precious, and things that you found annoying become so invaluable. And yet in retrospect, I realized that my grief, too, was irrational.
Did I really like it that she was rather obsessively needy and demanded my attention over all other things, especially my study and self-improvement, the moment I got home from work? Did I like it that she could not respect that I had days for myself to hang out with my guys? Did I really need to waste so many hours in a MMORPG just because it made her happy to have company?
No, no, and no. And yet all those things seemed precious to me in moments of irrational grief.
I think what happens is that we fall into solace, a comfort of what things are, so that when change happens, it feels such a sharp and abrupt blow. It /is/ a loss, a true loss, but a loss that we can grow from, and perhaps, even get into a better place because of the loss.