I (20s F) live in a shared apartment with my partner and a roommate (20s F). When we moved in, the agreement was that it would be a standard roommate situation with mutual respect for shared space.
My roommate started dating someone fairly recently. Within a short period of time, he began coming over frequently and staying overnight for multiple consecutive days at a time, every week.
Eventually, he lost his housing and my roommate asked if he could move in with us. My partner and I said no because that was not part of the original agreement.
Even after that, he continued staying over very often, and over a relatively short time it started to feel like he was essentially living here part-time without that being agreed on by all roommates.
My partner and I then brought up a boundary that overnight stays needed to be less frequent so the apartment could remain a shared space between the people on the lease. We did not say he could not come over at all.
Since that conversation, the atmosphere in the apartment has felt tense. Communication has decreased and interactions feel more awkward, but nothing has been directly said to me about it.
I have mostly stayed in my room since then because I feel uncomfortable in the shared space.
AITA for setting that boundary?
EDIT:
To clarify a few common points:
My partner lives in the apartment as part of the agreed household arrangement. This was established when we moved in and is not related to the current issue.
The concern is not about whether my roommate can have a partner over, but about the frequency of overnight stays over a short period of time and it functioning like an additional roommate without agreement from all people living here.
I did not ask anyone to move out or prevent anyone from having guests. The boundary was only about reducing frequent overnight stays so the shared living arrangement stays consistent with what was originally agreed.
I’m not going into further personal details about the guest or specific incidents for privacy reasons, but the concern is based on repeated patterns over a short period of time, not a single event.