You cannot do it alone. Period. Go to an AA or NA meeting. You're safe for the time you are there. Then go to another one, and another if necessary. Ask for help and mean it. Cut off all ties from your drugs; dealers, phone numbers, friends who use, all of it. Finally, get on your knees and ask whatever higher power you can muster up belief in (doesn't have to be God; can be anything, or anyone, as long as it isn't YOU.) and ask for help staying clean for just today, or just the next hour or even just the next minute. You can do this.
I know this is so tough for you right now but you can say NO. A very wise man on here used to say "when your desire to get and stay clean outweighs your desire to get high you will get clean" We have to change our playground and playmates. I know the high is no longer really there as you know this has to stop. Dont let fear keep you down. I used for a bazillion years and i just celebrated 10 yrs clean in April. I knew i was dying and my fear was my kids finding out my dirty secret and then they would of been left to pick up the pieces. I decided one morning that i had had enough and i would pick up my own pieces, and i did. It is tough but oh so worth it. You dont have to be chained to coke anymore. Time to take your life back, you are worth it~