It started changing when I got upset that she went out with another guy to a resturant alone. There was this small debate we got into, but that's over now. I eventually apologized because I felt like I was becoming too controlling...and then others began to tell me that that's not such a big deal. I haven't seen her physically in a week because she's been staying at her girlfriend's apartment and hasn't been sleeping on campus (I'm a commuter). And it's like every time I have some free time on campus and want to meet with her she says she's sorry she's about to go do something with this (girl)friend of hers.
I admit, I can't tell how seriously she's taking the relationship. This could all be about nothing though.
EDIT:I have to add that I'm slighty wondering about whether or not she's seeing someone else. Not because of the dinner...that's irrelevant now. But she's recently told me that she wants to stop having sex for now because she did it so much during the summer and last year that she needs a break (and it's not like we were a couple of jack rabbits before since we only had sex twice). So I'm wondering does she want to stop having sex because she's doing it with someone else? Or is this sincere? I know for a fact that there are a number of guys that come in and out of her "girlfriends" apartment. I also know one of the guys in her circle of new friends this semester...he used to be my roommate for a semester when I was a freshman. He's very open about the fact that he doesn't care about persuing women that are in relationships (and I'm sure I'm no exception)...and he's one of the one's that's always at the apartment (and sleeps over sometimes like my girl does). I also saw a picture of them two on Facebook where she's bending over directly in front of him on Halloween.
Am I just being paranoid? Or are there real concerns? Like I said, we haven't seen each other in a week, but have talked and texted a few times.