I can relate somewhat. A few years ago I had 2 friends, husband and wife, who smoked meth perpetually, and Corey (the woman) was utterly convinced her husband was cheating and having sex with another woman under the porch.. I'm not even joking. When he worked the nightshift one summer I would smoke with her at night and she literally told me she thought the woman was hiding under the box springs of their sofa.. there was no sense in trying to talk her out of it as she would immediately accuse you of being a co conspirator.. pretty sure she was schizophrenic, as she was literally always like this, even during dry spells, but the meth obviously would worsen it