The strange behavior and irrationality that Lori and Kevin exhibit may seem baffling to an emotionally stable adult. To better understand Lori and Kevin, it's very helpful to have a basic understanding of "
Cluster B" personality disorders.
Cluster B personality disorders include Antisocial Personality Disorder (ASPD), Borderline Personality Disorder (BPD), Narcissistic Personality Disorder (NPD), and Histrionic Personality Disorder (HPD). These personality disorders (PDs) often overlap as multiple co-morbid diagnoses. For example, a person can have borderline
and narcissistic traits. Here's a great website for understanding some classic behaviors exhibited by people who have these PDs:
Out Of The F.O.G.
Kevin is currently exhibiting many Cluster B behaviors. It's difficult to know whether these traits are 1) organic to him, 2) the result of substance use, or 3) mental health "fleas" he picked up from Lori. Kevin's ongoing denial of basic facts is ultimately a form of gaslighting to avoid taking responsibility for himself and his choices.
The denial of Lori's abusive history is the linchpin to keeping Kevin's fragile ego intact. If Kevin were to finally acknowledge the truth about Lori's toxicity, then he would be forced to confront his own toxic choices and toxic actions. Instead of taking responsibility for himself, Kevin is choosing to deny reality and blame others for his behavior. Externalizing the rage he experiences towards himself may feel "safer" to him. It seems that Kevin currently lacks the ability to gain insight from introspection because his ego is weak, his ability to cope is compromised, his psychological development is arrested, and, honestly, he may not have the cognitive ability to overcome his significant emotional deficiencies.
tl;dr - Kevin's narcissism, stunted emotional development, and stupidity are likely fueling his ongoing pathological avoidance of reality. He may also be experiencing dissociative and/or psychotic symptoms that are contributing to his deteriorating mental state. Substance abuse might be a factor.