You've taken the first most important step by admitting you have a problem. That's huge. Be proud of that. You really need to tell other people now. Alcohol is so much a part of our culture that avoiding it is incredibly difficult. Going out with your mates and not drinking (the "I'm on antibiotics" excuse is only good for so long) Tell them - maybe something on social media along the lines of I've got a problem, when I refuse a drink please don't try to force me to have one. Replace your crazy drunken stories with crazy sober stories- trust me they are still there. Figure out your own list of things you enjoy about drinking and how you can keep those things alive through not drinking. If you mess up don't beat yourself up about it and if it's only once, forget it. You're human. Give yourself one chance, and don't even feel the need to share your failure with anyone. Try to figure out why you fell off the wagon and vow never to do it again. But if you mess up twice, then you need to admit it: You've failed (this time). Go public with that failure; you'll almost certainly be inundated with offers of support and praise for your honesty. Take all that you're offered. Use that praise to start again.
If you have a job, tell your employers. Most reasonable employers will be totally supportive if you show that you are trying to quit. Before I left my last job, I represented somebody who was on a gross misconduct disciplinary for drinking in work. He was a fully blown alcoholic but completely in denial. It was so sad. He couldn't see there was a problem. He turned up for the final meeting, stinking of booze with four cans of lager in his bag. He was sacked. Had he been able to admit he had a problem and sought help he would still be employed.
Most importantly- do it for you. Not your parents/significant other. You've got to want it.
Good luck mate- I've lost family members and good friends to alcoholism.
Waaay too skinny, just veins remain 
