You've met his friends; he's met yours. Now it's time to add fruity cocktails and mix. Short of introducing your parents to his, combining your two sets of friends -- especially if they exist in very different worlds -- is one of the most nerve-wracking milestones in a relationship. And since summertime is party time, it's probably going to happen in the next month or so. Here are a few steps you can take to make sure it's not a complete disaster.