In public my boyfriend acts like we're not even dating?

I went to the movies with my boyfriend and a large group of people, about 8 all together. Throughout the movie it was cute, we held hands like usual and laughed a lot, but when the movie was over and we were all hanging out in the arcade things got bad. He didn't even talk to me barely, and I, being really social, was talking with everyone! He spent most of his time with this girl he's known for a long time, and was really good friends with, but I feel like it was flirty. They were throwing skittles at eachother, honestly?! Later on he said I "spent the whole night with" my best friend, so he went with her to p the time, which is a lie. I was actually doing a lot more socializing than he was, and I wasn't about to follow him around if he wasn't going to pay attention to me, so I made the best of it and talked to everyone else. I don't understand why he was acting like this, he seems really shy around me, but he's not like that at all when it's just us! Why is he doing this?