How do I get over a guy who I like but it turns out he has a girlfriend?

Ok, so I met this guy 6 months ago in college and we became pretty good friends. We hung out all the time and majorly flirted. We went out a couple of times and he invited me to his house to go sledding, just the two of us and last week he asked me out to the movies again. I agreed, we made plans, and the day before and day of he was telling me how he was all excited to go and for us to hang out together. A couple days before we went to the movie he told me his friend might tag along because he really wants to see the movie we were going to and he hadn't seen him in a while. Not wanting to sound controlling I said yeah, that would be fine. When we finally did go to the movie he met me in the lobby with his friend and told me they already had saved seats. We go into the theater and it turns out he brought 6 other people I had never met, and he didn't introduce me to any of them. Including his girlfriend, who I got to sit beside for the whole 2 hours. Was I completely off in guessing he might have liked me, and how do I get over this? I've never had this happen before and I really liked this guy, so I'm just wondering how to deal.