I have heard horror stories too. My son had one of his own in a previous rental. had a roomate he thought was watching his dog while he worked (for reduced rent). Turned out the poor dog never was let out of his cage or given food and water (het got a nanny cam that confirmed it) This roommate also destroyed parts of the house and the landlord kicked her out, but my son lost a thousand dollar deposit over it.
Anyway, our workaround is that my younger son and his best friend will be moving in with my older son. My younger son is a full time online college student so we will cover his rent while he is in school. His friend works full time, great kid. We are finishing the basement so both boys have their own space.
That sounds like a better arrangement. Was it you that has said your son would like to marry and settle down?