Regardless of how often you drink or how often you can go without, it sounds like when you do it can become a problem. So yes, I would support efforts to quit it all together, then you'll mitigate any future issues with blacking out, raging, etc.
To answer your questions, it's hard to say what qualifies as dependence. Sometimes that's very clear, other times and more often it's not. Go 6 months without, that might answer your question. If you find yourself uncomfortable with that idea, there might be an answer there too.
Regarding brain function changes, alcohol (and other drugs) can absolutely cause damage. Sometimes it's reversible, sometimes it's not. It really depends on the severity. Luckily, it's preventable.
Probably not what you want to hear, but that's my take on it
