It is possible - some people can do it for years and even decades. It takes a lot of boundaries and trust. Also patience with yourself and the alcoholic.
L is absolutely right, you have to accept them as they are, and not cling to the hope (in excess, of course you'll want them to quite) that they will one day stop drinking to the degree that it ends the relationship.
It is a very hard commitment to make as this means putting yourself through a lot of stress. Ultimately it comes down to how much you can handle and how much you care for the person - ask yourself if it is worth what you will have to live with compared to what you may lose and vice versa.