For a while, I had this exact same problem. It can get pretty bad locking yourself in your little dungeon for a dozen hours a day, every day (weekends included) when working on a big project. You can start to go a little mental if you let it get to you.
The simple solution is to just go out. If you're like me you need a REASON to go out, then generate a reason. I decided my reasons would be to work out daily (necessitating a trip to the gym), and 'life' outside the business just sort of spontaneously grows. It's pretty easy when you come to the realization that "Shit, I'm working too damn hard. I need to go out and enjoy some of this bling before I get too old to!"
The real problems start when you've developed all these outside influences and rediscovered the wonders of the external world, and work suddenly picks up and you're required to be chained to a desk again.