After a number of years together, an unmarried couple in a no-common-law-marriage state decide to consolidate households. The apartment renter (say $1000/mo) will move into the other's mortgaged house (say $2000/mo mortgage).
They decide 1) to split the savings, which amounts to the rent on the apartment, thus the non-owner will contribute half of that rent ($500) towards the mortgage/taxes/whathaveyou, 2) split the utilities, and 3) the owner will always be 100% sole owner regardless of developments.
While the owner doesn't want a contract, the non-owner is willing and thinks a contract is a very good idea for the benefit of the owner.
How might a cohabitation contract benefit the non-owner in the event that 1) the relationship ends disagreeably, and 2) the relationship continues but a lawsuit is filed against one or the other by a third party?