B’s name is not on the mortgage, the utilities etc so is losing credit proof needed should B move out. Say, A dies? Basically a roommate agreement would work. A needs a written agreement so it’s easier to evict. I’ve thought of this stuff, not as a love interest, but an actual roommate. What’s the fair rate? Roommates.com will show places rates in your area. I hope that’s net income and both are contributing to their retirement funds. Also, B needs a better job, maybe more education or certification.

Where things get bothersome is home maintenance and improvements. That’s equity responsibility. So I believe one has to determine if B is equal to a roommate paying rent; in which case, the financial burden and yes the fun decisions are A’s to make. Then utilities. A should provide the past years usage and payment. Can the increase be attributed and paid by B? Then food/chores. And as any good attorney would ask A, would you feel differently if B won the lottery?