I'll bet many of us were "the next girl" for someone else, and they asked the same question about us and our alcoholics.
"The next girl" may be treated better, for a time, sure. If were were mistreated in the beginning of the relationship like we were at the end, who would engage in the relationship at all?
Without working some sort of a program to better himself though, the facade will only last so long, and instead it turns into a question of how much will "the next girl" be willing to suffer through before she's done, too. It's the same roller coaster we were on; it's a remake of the same movie, with the same cast but a different leading lady.
You're a smart woman. You already know the answer to this question. It's okay to believe the truth.