He has not changed. Now he may not have "sexual urges" but then he might have a medical reason for that and/or no opportunity.
Well, he had someone at his disposal to satisfy his sexual urges for 18 years, if he stopped using her for that purpose then something must be different. I don't see how you can argue that he hasn't changed when his behaviour clearly had.
I think that if you are going to take that approach it would make more sense to argue that his fundamental "issue" hadn't changed, but the way it manifested itself had as his subconcious desires became reality. I bet if you dissect this guy's psyche you are going to find an underlying theme of family being expressed in a twisted bizarre kind of way. In his early years he was missing something, in adulthood he set out to find it using whatever method he saw fit, and in middle age found it (and also found out that he had something to lose - oh, the irony! ). That might sound like the journey everyone takes (well, most people anyway), except that he was crazy, so his journey to that end wasn't like yours or mine.