My roommate's partner has been staying at our apartment 5-6 nights a week for the past two months. They don't pay rent. I brought it up to my roommate and said I thought it was fair for the partner to contribute to utilities at minimum, since our water and electric bills have gone up noticeably since this started. My roommate said the partner is "just visiting" and that I'm being unreasonable — they're not using "that much" extra. But they shower here every morning, do laundry here, cook here, and are here when I wake up and when I go to sleep. That's not visiting. Their side: we have a two-bedroom apartment and the partner stays in my roommate's room, so they're not using any extra space. Guests are allowed under our lease. My roommate thinks I'm trying to control their relationship. I don't want to control anything. I want the utility bill split to reflect the number of people actually living here. Am I wrong?