Maybe in the opinion of the homeowner, but in the eyes of the tenant it is very relevant. Understanding your supplier’s alternatives is a critical part of negotiation. The info could be estimated if not outright determined.
How valuable to you is your friendship? You may want to take notes and have your landlord initial notes as a quasi lease. Many a friendship has ended on acrimonious terms because a legitimate business transaction was clouded by friendship.
I’ve played this game many times before. At first, I was sharing a house with a friend. Then my brother and his girlfriend moved into one bedroom. So that made 4 people in 3 bedrooms. We eventually said that my brother, who was paying for 2 people, had to pay less than 1/2 ('cause he only had 1 bedroom of 3, not 2 out of 4) but more than 1/3 ('cause she was using common space too). He paid 1/2 (rather, 2/4) of the utilities.
Then I bought a house. I wrote out a lease agreement that said there were two rents- one for when it was just the two of us, another for when there were three of us. Hell, I threw in rules about how long dishes could stay in the sink and which cabinets they could keep food in, so I covered all bases.
The question you have to ask yourself, OP, is “What am I paying for?” It could be that you’re paying $500 for a bedroom and shared bathroom and your friend/owner (not legally considered a landlord if he lives in the house) is overdelivering. Or it could be that you paid for two bedrooms and a private bathroom and now he’s underdelivering.
If it wasn’t specified which is the case, how do you know? Look elsewhere and compare prices. If you’re getting a good deal, then you were probably paying for the 1/shared and were getting a bonus all along. Then you should pay $500. If you’re paying market rate, then he’s underdelivering and should cut your rent.
Absurd. If the owner bought the house outright and has no mortgage does that mean OP gets to live rent free? I don’t think so.
What the owner chooses to charge is entirely up to him based on whatever he wants. His monthly expenses are of no consequence to the OP at all. If the OP does not like the rate being charged, he is free to live elsewhere.
It’s not so much a matter of whether you “deserve” a rent reduction, as whether you are capable of negotiating a rent reduction.