Should i spk to my friendds about the fact that i self harm ??? or hm i dunno .( help ? )?

okay well first i would just like to say sorry for all the wrong spellings nd stuff ( because i know that anoies some people :P ) and well basicly i have bn self harming for about 2 years or somthing like that and im around my friends alot so they have managed to figer out that i self harm but theyv never told me that they know about it and i know that they were spking about it behind my back to my sister ( then my sister told me ) should i spk to them about it or wait untill they bring it up ? ( if they ever do ) but i wouldnt know what to say and i cant stand being with my freinds now because i just always have the horrible thought that they know in the back of my head and i just feel like im anoing them and im anoing myself . once agein relly sorry about the spelling and bad grammer im kinda sleepy . sorry if iv waisted ur time :S oh and a reson why i havent spoken to them about it is my bestfriend bleives that all people who self harm or have mental ilnesses are just atention seekers so shed probs ignore me if i did properly tell her .what should i do ?