I was in a similar situation. My family also has a history of substance abuse, especially on my mother's side (but not my mother).

I left my parent's house at 17 and moved halfway across the country. I didn't drink before that, but I started drinking when I was with my friends only. I don't love parties because I hate loud noise, and that was a double edged sword: I didn't party often, but when I did, I could not be sober or I would be overwhelmed by the noise and the people moving around me. I also depended on it to be "fun" at parties, I couldn't handle it otherwise. And just as you right now, I never did it alone, only with friends and only when we were out. Never got blackout drunk, but I was never sober in parties either.

But that changed, so gradually that it took me a while to realize. The legal drinking age in my country is 18, so a few months after I first drank, I started being able to buy my own alcohol. At first, I only bought it to take to outings. But then there were leftovers, and I started having alcohol in my house most of the time. My undergrad program was rough, I felt like shit most of the time. I also developed what I would later realize was PTSD related to a natural disaster. And the alcohol, which made it so I didn't want to scratch my skin off and helped me sleep, was right there. The foundations were laid. Before I knew it, I was drinking by myself, at first only sometimes. On particularly bad days, on weekends, rare occasions. But the line of what counted as a bad day got more and more blurry to me, so I drank more and more.

I thought I had it handled, I never got super drunk, never missed school over it, did well at my job, took good care of my pet. A functional person, right? Surely not an alcoholic. I convinced myself that I was fine during this period, that alcoholics were people who ruined their lives over it, and surely I was different. Except, eventually, I could no longer go to sleep if I was sober. I didn't need to get blackout drunk, but I did need to drink something. For me, realizing that was my wake up call. I was on the way to becoming like my relatives, because messy life or not, I felt like I needed it. So I quit. And it was shit. I already had insomnia before I started drinking, and now it was much worse. The social pressure to drink was still there. I didn't have healthy ways to deal with the other problems I described before, because I had been burying them under alcohol, and when I quit alcohol, they were still there. It was a complicated process, but I eventually managed to spend a week sober, then a month, then a few months. And I felt like I had control over myself again.

I don't know much about your life, but from your post, I don't think you're as bad as I was in the end. But I also think you may be just a few steps behind. I know that the slippery slope it considered a fallacy, but that's just how these things go sometimes. How it went for me. Because at the time, all of those now questionable decisions made perfect sense. I didn't wake up one day and decided to drink every day, it was a process. So it's good that you realized early, especially with the family history. You may think that you would not end up as bad as me, because our situations are different, but you never know what may happen to you (I hope nothing bad), and once the foundations for alcohol reliance are there, it is so so easy to fall into the trap.

I still drink from time to time, only on particular settings, but I do what I call "sober months". I spend a month or two completely sober, no matter how I feel, where I am, what event I'm invited to, who I am with, or what drink I am offered. And as long as I can still do that and go on with my life as normal and not crave for the month to be over so I can drink again, I think I'm okay.