Scary that the military enables alcoholism like that, but completely understandable that any latent drinking problem comes out with the stress of service. AND the drinking culture that exists when off base and off duty. I've known several Navy and Marines who had serious issues. There are many at the gay bars in San Diego in the grips of some pretty serious addiction.
Just don't celebrate the end of your service with a trip to the bars with buddies, military or otherwise.
It may or may not be a good idea yet, and you may be busy dealing with the aftereffects of lots of alcohol, but getting sober and sharing your experience is key If and when it's appropriate and you're ready, telling your family and loved ones can be helpful in keeping you sober, as it becomes harder to hide it from people if they know. Believe it or not more people than not are supportive and proud, especially family and romantic partners.
You may find that this journey is a tough one. So is being a Marine. You've proven that you've got the strength and courage to do this. You got through training and either combat or the possibility that you would have to be in combat.
I've known Marines, and there's a certain bond in the Corp that's hard to replicate, and was tough when they finished their service and it started to dissolve. Finding others going through what you are going through might make it much easier. They'll get it. Other groups are pretty essential, AA or otherwise. Having a plan to get and remain sober is crucial, there's plenty of information about this on the site.
Congrats on your 3 days. If you can make it the start of the rest of your life you will look back on this moment, as difficult as it is now, with humility and pride.