There are many things you could do in summer, even if your friends are away. Here are a few ideas:
- Get a part time job - not all jobs have to be boring and dull, there are plenty out there that can make you a bit of money as well as giving you something to do.
Maybe have a look around your local town to see if and shops are advertising for staff, or look into seasonal summer work like selling ice cream or picking fruit. Not only could it be fun, but you can also make lots of new friends! 
- Join a club- There are often many weekend or evening clubs or classes taking place in an area that most people don't even know about. From sport to painting, charity work to social clubs, chances are there is something that you will enjoy.
- Give yourself a project- Instead of just sitting at home wondering what to do, set yourself something to do everyday. For example you could make a scrapbook out of old photos and other things you have laying around, or you could redecorate your room. Setting yourself a goal will give you motivation to do something productive and it will also keep you busy.
- Exercise- Although this may sound dull to some people, after exercising you will feel great, especially if you set yourself a target to reach at the end of summer. Not only is exercising good for you but it can also be fun!
I hope these ideas have helped, and your friends will be back before you know it!