It is possible to be happy and sad all at the same time!

So my oldest nephew Josh and his wife had their baby boy Henry today.  They already have two daughters and this is the last baby they intend to have and they were of course hoping for a boy.  I am really happy for them.  but at the same time I can't help but wondering why I wasn't able to have at least one child with David.  Why I am now all alone in life.  Friends/family isn't the same thing after a spouse has died.  They can only fill up so much of my time before they have their own lives to deal with.  It's the happy things that make me feel the most alone in life.  I miss David so much and it hurts so much and it's a double edged sword.  I want the pain to go away but I don't because as long as I am hurting I know I am still remembering David. =(