I'm going to suggest a book I found VERY helpful as I was going through a couple of divorces and the breakup of a LTR: Uncoupling: Turning Points in Intimate Relationships, by Diane Vaughan.
That was my "Bible" the way some people love Co-Depenedent No More. Uncoupling is the product of a study the author did on the breakups of long-term relationships, from the perspective of both partners. The "initiator" is the one who wants to leave--and has come to that decision in his/her heart long before the "partner" really has a clue there is a serious problem.
What is awesome about the book is how most breakups (and she interviewed people who were married or living together, gay and straight) follow a fairly predictable course, with one person being the one who wants out and the other the one who wants things to stay the same. What she learned is that by the time the "partner" (the one who is being "left") finds out the other is serious, the whole process gets dragged out further by promises and efforts being made to "save" the relationship, which are probably doomed by the fact that the "initiator" wants OUT and is likely to sabotage those efforts (not necessarily consciously).
She has many, many interviews with "initiators" and "partners" about what was really going on during these various stages of breaking up. I liked it because it validated my own experience and it also helped me to understand where my partner was coming from and how he might be feeling.
It doesn't have anything to do with alcoholism or addiction per se, but since you seem to have made the decision you want out regardless of his drinking or not, you might find it a helpful read.