Sometimes the best thing you can do for someone you love is step out of the way and turn them over to their Higher Power. You can't make him sober, he won't do it for you. That's not how it works. The sober guy you love and the mean drunk are the SAME guy. There aren't 2 guys in this picture, he is one and the same. As the disease progresses, and it will, you will see less and less of the sober guy you love.
Find an AlAnon meeting near you, and attend a few meetings. You don't have to share if you don't want to, but listen to others. AlAnon is not for the A in your life, it won't help you get him sober. It WILL help you realize that you have to focus on YOUR life. You are only 20 yrs old, there is no reason to settle for a life of chaos and heartbreak. It's not easy, but the best thing you can do is walk away and find your own serenity. ((hugs))