It happens. When you breastfeed your baby not only baby but you too feel bonded with her, and when you wean her off, you yourself get the feeling as if you are going away from the baby. It is all natural I guess. It is also called post-weaning depression. Read this article to understand it better.
http://www.bellybelly.com.au/breastfeeding/weaning-and-depression-post-weaning-depression/
http://www.huffingtonpost.com/entry/weaning-breastfeeding_n_5154681.html?section=india