The Fair Housing Act by its terms doesn’t apply to rentals below four units, and at least one federal appellate court has determined it doesn’t apply to roommate selection: https://sharinghousing.com/what-the-fair-housing-act-means-t...

There’s a fundamental tension between certain non-discrimination laws and freedom of association. The more intimate the association in question (with roommate selection being much more intimate than leasing in a large apartment building) the stronger the interest in freedom of association.