I hate the phrase, sex addict.
Though some tiny minority of humans may be so obsessed by sex that they are incapable of controlling their thoughts, actions and behaviors, making a disease out of bad choices does little good.
The fact is that most people obsess about sex. Men in particular think about sex every few minutes. Men masterbate many times a week and men fantasize about random sex partners nearly every day. Finally, given a chance, most men look at porn frequently. Study after study of human sexuality confirms all the above. People should not live in shame for the above behaviors.
However, there is a difference between thinking about sex and seeking inappropriate sexual partners. We should be judged by our behavior, not by our darkest thoughts.
To get to your question, "is it possible for him to have gone good?", I will respond with a question - are you talking about thoughts or actions?
Yes, it is possible for people to mature and to understand the consequences of our actions - and by doing so, to change our behaviors.
Change those thoughts . . . that is less likely.
That said, interest in sex changes with age, mood, health - so maybe. But you can't expect these changes to be permanent - unless he had a major health or lifestyle change.