I wanna know y i m feeling so lonely whn everyone is around me and y do every one keep a distance with me??

i am around 24 yrs and i hav lots of frnds but very few r close to me and now they are far apart from me as they have all settled in life. i was close to my sis also. but now she is also away from me 'cos of her job. very recently she is showing some distance from me. sometimes talking very harshly that makes me real sad. i hav a frnd whom i love very much. at first he too loved me or did he show tht he loves me. but after a few weeks he ped his course and now is a professional. i love him so much. he knows that. but now he too gets irritated while talking to me. i dont know wht to do. i m very sad in every way. i cant concentrate on my studies or job. can anyone out there help me out of this situation????