Is it "faux pas" or bad in general to take a person other than your SO to a wedding?

I’m going to a friends wedding the first weekend in September. My girlfriend is moving back to college the week prior to that, and doesn’t want to leave school the first weekend back and miss out on meeting new people in her new dorm. I wish she could go and am sad she can’t, but I understand. So the idea occurred to me that I could just take a female friend of mine (no one in particular, just that I could take someone else since the g/f couldn’t go). Well I jokingly asked my g/f if she would be upset if I took someone else, fully expecting a sarcastic response about how she would be heartbroken or something… and much to my surprise she really was very upset.

In particular, her first response/question was to ask if I would take a specific girl. To which I replied that the thought had occurred to me (which as I had stated before, I had thought about it but no one in particular struck my mind). Quick back ground about that specific girl (we’ll call her tina)... my g/f and I broke up for about 2 weeks around 2 months ago. Huge fight, yada yada, thats not the pertinent part. During our “separation” at the great insistence of a friend of mine I went on a “date” with Tina (we got coffee and talked for like an hour). I honestly didn’t want to go, but I knew I couldn’t sit there and pine over my g/f. I didn’t forsee any romantic future with Tina (at least anytime in the near future as I was and still am thoroughly in love with the g/f) but she was a really nice/cool person so I continued the friendship aspect from there. We’ve hung out a few times and chat via text. Early on Tina still had the inclination that this may end up romantic, but I told her that I wasn’t over my g/f, and then when the g/f and I got back together I told her we were trying to work things out (which is where we are now).

Its worth noting that Tina would know myself and two other guests at the wedding, and I know many of the people who will be in attendance. Ignoring for the moment that I hadn’t picked any particular girl, let alone Tina, or let alone that I would go with anyone else, am I in the wrong for thinking its ok to take someone who isn’t my SO to a wedding, even if its someone like Tina.