My baby is not a baby anymore, he's such a big boy...

We transitioned my 2yr old to his new big boy bedroom today. I was expecting lots of tears and upset, but they only came from me :( I keep trying to go into the nursery to clean and organize and transition for the new baby due is three weeks and I just feel sad. I keep thinking about my first son and all our memories. It is a strange kind of mourning to have a second child.....saying goodbye to a chapter of life, while trying to prepare for the next. The difference 27 months makes.