Is there a diagnosed mental condition where someone can alter their perception of reality just by convincing them self something is true? I’m watching the relationship of a close friend of mine deteriorate because his wife is absolutely certain he cheated. For clarification he has never cheated on his wife. She will name specific names of women she is certain he slept with. She will tell stories of interactions with the women that never happened. This is most evident because the story changed slightly from time to time when it was told. It has basically turned into he has slept with pretty much every woman they mutually know. To her, this is reality.

If he challenges her and asks for proof or denies what she says then she gets extremely angry. Yelling is very common. She will put him down and call him a cheater and some pretty hurtful names even though none of that has happened. Is there a name for this type of behavior or condition? Where someone believes something so much that is their new reality. Psychosis seems a little extreme.