Welcome! Say what's on your mind. We're glad to have you.
That's more or less how it runs, no "one beer." Whether you're an alcoholic, abuser or just stuck in a habit, all of us at some time or another have had to ask the question "is it worth it?"
You're right that there is fun in drinking, but at the same time there is also fun in having a girlfriend, health and a job, right? You might be able to keep the alcohol, the girl and the job. However, you've already suggested that alcohol tends to or has threatened the latter, which seems to suggest you're gambling a bit by drinking. As for your health, I think that's an either or decision since you say you're already having some problems.
A whole lot of alcoholics I've talked to and myself included have all been in this very same position. We were drinking hard a lot and we were starting to make a lot of big mistakes and lose things we didn't want to. What we did was try to devise plans where we could have both. I've heard some pretty elaborate stuff. And in every case they fell through.
I am definitely not saying you're an alcoholic or that you're going to be. I just think a good bit of advise you can take, not just from me but from 100s of people I've talked to, is that there's probably no way of getting around the trade-off. Or at least there's no escaping the risk. If you can't cut down on the beer you drink at one time, it's the experience of alcoholics that one has to stop or gamble with one's health, relationships and jobs.
Alcohol is complex, and you shouldn't take what I've said as gospel truth or anything. In my opinion the best thing is for you to figure this out on your own. I realize I got a little blunt in my message and that's only to kind of warn you of one of the stumbling blocks a lot of people I know and I had faced when we were trying to figure things out. I think if you're just really honest about it, you'll be better off than I was.
Good luck to you, and glad you're here.