Well, I guess no one can tell you why people leave you. Everything is transitory... People, friends, boyfriens/girlsfriens, in special drift way. But you can always try making new friends... Worrying about it don't really help you in any way. That's not a way of solving your problems... but stoping thinks about your situation is a way to deal with it, and then begin trying to have someone more permanent in your life!