I too believe Nick was genuinely put-together, mentally stable, and a good dad and husband before the Imholtes and the coke. There probably was a latent personality disorder that hadn't manifested yet, but addiction and hedonistic lifestyles change a lot about your personality and your judgment, and tend to push responsibilities aside. So I doubt the house was a hoarded, filthy mess before this saga when Kayla was more interested in domestic duties than ketamine.
I don't know why Aylawgz think he couldn't have changed entirely as a person after drugs were introduced.