I think the ending implies that he is still the same guy, and he is never going to change.
That's a pretty dour way to look at things, unless I'm misunderstanding you. I took the ending as "love redeems" and that Chuck was ultimately wrong about Jimmy as a person, even though it took a lot for Jimmy to hold himself accountable. I guess you could look at it that it's in his nature to be self-destructive, but even then he was able to own up to it in the end.