I just left my "great guy who just had a drinking problem." I was in the same boat as you - I immediately noticed he liked to drink a lot, and quickly it became clear he was an alcoholic. He told me he had been to AA, had a DUI and a couple other alcohol-related arrests under his belt. I also didn't want to be "ultimatum girl," so I held off on that for a while. I eventually gave that a try a few times. Didn't work.
I spent much of the relationship miserable, wondering if he'd be drunk when I showed up, trying to figure out my boundaries (which I'd establish, he'd cross, and then I'd just move them back to accomodate), dreading him meeting my family and friends for fear he'd get drunk and make an ass of himself, being afraid of what he might do while drunk, and trying everything I could think of to influence him to be sober.
Long story short, the heartache and pain were enormous. I wish so much that I could go back to each moment that I considered leaving him and just do it. I realize now that I hardly even had a relationship... I was there to create a sense that everything was OK and normal, for him to show his parents that he can't be so bad if he has a girlfriend. He had no room to care about me. Everything was about the alcohol. You'll come to realize the same, both through your experience and by reading these forums.
So, if you're not sure what to do, what I would suggest is this: Take care of yourself. Be selfish. Every time you wonder how he's doing, check in and see how YOU'RE doing, and know that you have the power to change YOU and the things around YOU.
ETA: The best way to tell him to get help? There isn't one. He can't hear you right now, and won't be able to until he's well into recovery.