I'm right there with you. We found out yesterday we are having our 5th boy. I wanted a girl so badly but this is our last one so it will never happen. I haven't called any of my friends yet to tell them, I just can't bring myself to pick up the phone. I thought about announcing it on facebook but can't even do that.
I know it gets better. I thought our 4th would be our last and I did get over it. It took years though, I'm not gonna lie. It helps me to think about how I'll never have to buy tampons for a daughter or have to deal with all those female hormones and emotional teenage years. Boys tend to be easier when they are older.