Why do we miss people?

Why is it that we miss someone in life. I for one person tend not to miss much in life, normally I am content and happy with whereever I am, if not I try to make my surrondings happy :). Ofcourse there are days that I miss being at home and likes but soon I get out of it.
But now I miss someone, someone very very precious to me and that is my first born baby.
I know he is happy at his grandparents, absoutley sure he has no reminisince of me but I miss him so bad, at times I have tears in my eyes when I think I am not with my baby.
Well, what's stopping me from leaving everythign and going to him, you may ask?
Here is where the practicality sets in, we will be together after 3-4 months, till then I'll have to live with his memories :)

Love you my baby.