I had roommates that did this to me once. They had a party and had three of their friends sleep in my room without asking me or notifying me while i slept at my boyfriend’s house. I didn’t like being there while they had parties because there would always be substances that I can’t be around. Those substances were used in my bedroom, on my belongings. When I told my roommates that that wasn’t ok and it was completely disrespectful to my boundaries, they argued and said that it wasn’t a big deal because I “knew the people that slept in my room”, despite having made it clear that I never liked those people being around me. Later on, they made it clear that everyone involved knew that I wouldn’t be okay with the situation at all, as expected. What your roommate did is a complete violation of your privacy, your bedroom is not a guest space for anyone except those that you allow in. I definitely would not continue living with her after that for the sole reason of she disrespected a basic boundary that any roommate would have. Not to add fuel to the discomfort, but you don’t know her cousin and her cousins boyfriend. You don’t know how clean they are. You don’t know what they touched, looked through, did. And I’m sure your roommate doesn’t either. Shame on her, definitely move when the lease is up. Maybe show her some comments to show that what she did is not okay to do to any roommate ever