Knowing the person you love is in there somewhere but not being able to reach them.
What person? You make it sound as if there was someone else other than the alcoholic you dated for 9 months. He’s doing and saying all the things alcoholics say, it’s your fault he drinks, it’s your fault he can’t get sober, it’s your fault for not supporting him- bla- bla- bla. His issue of drinking was there long before you came along and will be there long after you have moved on.
You want a deeper understanding of his thought process but I think it’s your own though process that needs analyzing. 3 months into dating someone who shows you that they have a drinking issue, who shows you anger when questioned about his drinking yet you stayed around. At 6 months into dating things declined even further to the point that he became everything you didn’t want, yet you stayed around? Those staying around questions are what you need to work through, your whys so that you do not repeat picking the addictive person again to date and what all of those red flags in dating mean so that you end things at the moment they pop up.