I (20 m) and my gf (21 f) are having a bit of an issue regarding a boundary I want to establish. For context, this happened a few weeks ago, and the boundary is, as the title says, that I would like her to not go to other men's apartments alone with them. We attend the same university, and finals are coming up. During the incident, I was sick and bedridden. She was studying in the library when a guy she had recently become friends with asked her to go back to his apartment to study, and she went with him. I did not know this was happening until I got a text saying, "We made brownies.". I was a bit confused and too sick to gauge what she meant, so I replied, "At the dining hall?". And she said, "No, at my friend's apartment.". I asked, "Who are you making them with?". She then said, "With Tobey, since we finished studying for our psych exam.". I left it at that as I was still pretty sick and wasn't in the headspace to approach the situation. It was just her and Tobey in his apartment. This leads to earlier today, where I expressed to her that it made me uncomfortable that she would go to Tobey's or any guy's apartment alone and do date-like activities together (me and her cook/bake together as a date night activity). I said that since we are in a relationship, it is disrespectful to put yourself in such a position and that I would not put myself in a similar position out of the respect I have for her and our relationship. She then said that she did not partake in making the brownies and that it was Tobey who made the brownies while she continued to study, which didn't make sense as, why say you were making brownies in the first place if you actually weren't. Then she went on to say that she felt like I do not trust her. This is the only boundary I want to put up, and I have never doubted her as I know she is a trustworthy person. I have no problem with her hanging out with anyone anywhere, just not back at their apartment alone. She also went on to say that this boundary, not hanging out in other guys' apartments alone, makes her feel like she cannot be herself without second-guessing whether she is doing something wrong. I spoke with a few friends, my parents, and my sister to receive some clarity on this, all of whom said I am not doing anything wrong by enacting this boundary as it's the bare minimum in a relationship. However, I also don't want to hurt my gf by making her feel like she cannot be herself, so I'm stuck between a rock and a hard place. I want to do right by her and want her to be happy, but I feel uncomfortable about this situation and would like either a harsh reality check so I can get my shit together or reassurance that this is an appropriate request.