This is a red flag that you are wise not to ignore. He obviously has a drinking problem and before you marry an alcoholic you may want to go to the AA site and read. Educate yourself and then you'll start off your conversation with the knowledge you need to broach his problem with him. You'll not be able to convince him in anyway so don't EXPECT that your going to be able to control an outcome here. Hopefully he'll have a light-bulb moment and be able to and willing to quit on his own. Don't get your expectation up on that outcome though.
I just hope when he hits his rock bottom that that rock bottom for him is not killing someone while driving drunk.
If he ever asks you to marry him, don't unless he's fixed and is over his addiction and stupidity. Remember you can't fix him so don't marry him when his actions are so angst inducing to you. JMO.
“The willingness to accept responsibility for one’s own life is the source from which self-respect springs.” ~Joan Didion