I (24F) share a two-bedroom apartment with my roommate (24F) that we both rent equally. We've lived together for almost a year now with no real issues. Lately, her boyfriend has been staying over more and more. At first, it was a few nights a week, then it became basically every night.

Last week, she sat me down and asked if it would be okay if he just officially moved in to "save him some rent" and "make things easier." I asked if they were planning on paying extra for utilities or splitting rent three ways, and she said no, it would just be the two of us on the lease still.

I told her I wasn’t comfortable with that. I didn’t sign up to live with two people, and honestly, I like having my own space. She got super annoyed and said I was being selfish and not supportive of her relationship. She even tried to guilt-trip me by saying, “If you really cared about me, you’d want me to be happy.”

Now things are really tense between us, and a few of our mutual friends are saying I should just be flexible because "it’s not a big deal."

AITA?