What can I do to stop being so sad and lonely?

For the past while I’ve been feeling so sad and lonely all the time, im not sure if im depressed because I dont cut myself or anything and I dont want to kill myself, I just want to get away from everything (friends,school,family, just everything) and I have no reason to be depressed, I have a nice house, great friends, I just always feel sad, but the worst part is, 2 of my best friends suffer from depression, and they are always telling me how they feel, and I dont mind at all, I love helping them, but it just feels like I never tell anyone how im feeling, so I have sooo much bottled up inside of me. everynight I take my dog for about an hour long walk, just because that kind of makes me feel like im getting away from everything, but I often just feel worse when I get home. And also lately I always want to drink, my dad is an alcoholic, but I dont see him anymore, but im just worried that I might get addicted to alcohol. Im only 15 and I get drunk pretty often, buut life just feels so much better when im drunk or buzzed. So can anyone tell me if im depressed or just stressed? Or just give me some kind of good advice, juust to help me somehow? it would be much appriciated - xox j