Hello and welcome Orion!
Yes, cohabitation before marriage is forbidden in the Baha'i Faith, and for the purpose of protecting the believers, those who violate it could be subject to administrative sanctions (not being permitted to e.g., contribute to the Baha'i Funds, attend Feasts where administrative matters are discussed, to have a Baha'i marriage, to vote or be voted for, etc.). This might not be universally familiar or applied in all local communities, but it is what it is to happen if a believer persists after being lovingly told of the law.
There are some edge cases as I recall where this would not apply (like maybe an elderly woman renting out a room, etc.), but that does not seem to apply here.
While the Baha'i Writings would agree
that it is wise and praiseworthy to take enough time to get well acquainted with the character of the person before undertaking the serious commitment of marriage (as we just were discussing in this forum
), it is not necessary or even helpful to "sample the goods" so to speak, if this is meant in a physical sense.
Although Baha'i marriage is to join both the physical and spiritual
, it is the spiritual which is seen as having primacy, with the physical being of lesser importance given its impermanence. When two people genuinely love each other, with a commitment born not solely out of mere fickle passion, but out of a tender friendship and commitment to adhere to heavenly principles regardless of feelings, they can overcome all issues together. The spiritual love naturally and beautifully becomes manifest in the physical realm as well.
If one has problems in the area of sex, one may seek the advice of doctors or counselors, but much of physical "compatibility" relates to the willingness of each to adhere to the "Golden Rule" and that springs from one's character, something which one can (carefully) observe outside of a physical context.
Indeed, in my opinion, the physical intimacy before marriage is in fact a barrier to objectivity when choosing a spouse; one becomes tied emotionally and focused on trying to "make it work" (with reluctance to decide against the person due to a fear of guilt at leaving or of uncertainty for being left alone) rather than taking the time to see fairly whether the person is really suitable.
And on the other hand, if one later decides against the person, it can cause serious heartbreak and bad feelings between either or both and future spouses, something which the unity of the Baha'i Faith is meant to help us avoid, and moreover cause one to sully "that unique and priceless bond that should unite man and wife." (ref
This is similar, in my opinion, to the Baha'i view on voting which while endorsing elections, prohibits campaigning. We are not well served by the person exposing for us external matters such as their promises, self-praise, or pandering, but rather by witnessing their character in action, by their demonstrated experience of love and service to their family, friends, and community.
As far as day-to-day life, while daily living does indeed expose one to another's character, I think one can witness much of this by working together in service with the other person, and in the company of others as well, whether family, friends, or community.