Upon further research, it looks like Steve does NOT have delusional disorder as previously thought, but actually Schizophrenia. The reason it's not the former is because that's classified as having NON-bizarre delusions, i.e. stuff that could really happen, like being poisoned or having a lover be unfaithful, etc... Schizophrenia on the other hand, encompasses having bizarre delusions (Such as thinking you're a gardevoir and a porygon is a meowth), and hallucinations (such as seeing green articunos and tooth clefairies).
This also means Steve's going to be put on medication.
Anyway, I'm doing more research on this, but I'll keep you Jacksons (and other interested parties) posted!