you are not blowing things out of proportion.
it does sound as though he may be having a relapse (whether off his meds entirely or his new meds not being quite right yet, you dont know).
i spent 3 years being the sole carer of a schizophrenic and she had a relapse towards the end of our 3 years together. same sort of warning signs, defensive when asked about meds, inappropriate behaviour etc etc.
him turning up when told he cant stay is also a bit of a red flag under inappropriate behaviour.
basically if he is doing stuff that is out of character from the time you have known him, then you are right to worry.
in my experience, you cant bribe or ultimatum a person to take their meds.
like a poster ubove said, until they are at peace with and have a good understanding of their illness, then relapsing is very common.
i feel for you, its very distressing.
i think what you are doing is all you can do. say he is not welcome until he is back on meds and an even keel again.
good luck.