I also started grad school about two months ago and have been facing similar struggles. St Andrews Lynx has some excellent suggestions.
Some optimism: It may very well be the case that your advisor will be around much more once classes start, especially if he will be teaching. Many professors receive no salary during the summer. Furthermore, due to teaching obligations and assorted administrivia, it can be difficult for professors do much traveling during the academic year. Thus, summer is the perfect (or the only) opportunity to take extended family vacations, visit collaborators, etc.
Don't panic. Fall's just around the corner. And if your advisor was very attentive during the application process, chances are he will once again be attentive once the school year begins.