I can't tell you how to know for sure, but I will tell you a little bit about my experience.
I have been browsing this forum for a few months now, because I was concerned about my drinking. Nothing really bad had ever happened*, like a DUI or an arrest, but I was feeling like it might be a problem. I vowed to cut back and was glad I was just even reading up about whether or not it was a problem.
Without even realizing how bad it was getting I was drinking more and more, feeling more anxious, still thinking all I needed was to take a break. Then really bad stuff happened. Like getting arrested bad stuff. Like getting 5 staples put in my head for a self inflicted head wound. I had no idea that's where I was headed when I first started browsing here, and without trying to have too many regrets I wish I'd taken the whole thing more seriously the second I googled "alcohol abuse".
I was really good at fooling myself, it's really worth it to try and be as honest as you can with yourself about your concerns.
*just this short time sober has shown me that lots of bad stuff was already happening, I was just too deep in denial/too drunk to acknowledge it