How to get over being lonely?

ok he obviously needed to get away maybe when he does what he has to do he will be back and if so then make a move but for now he is gone so go out with friends enjoy life, take a week or two holiday during the summer,just have as much fun you can it will help you not think about him as much

There isn't a speedy process you just have to let it take its course. Maybe try to go out with your friends to a club or a bar and just have a casual talk with people. The more you are preoccupied the less time you will stop thinking about him. But no one is going to replace him so don't go out trying to find someone similar. If you are not ready to go out then take up a hobby if your not a social person.
You could also write out your feelings through poem of songs, even if your not a great painter, paint something. I always find it best to write out how I am feeling. It helps. Do you know why he left?

Whatever you do don't get overwhelmed if you feel you need to let it out, I'm sure you can talk to a friend don't keep it bottled up inside.