Is it normal to feel so betrayed?

My boyfriend and I have been together for over 2 years and since August we have been living together which is wonderful. We have never seriously argued and there has never been any cheating or any kind of stuff like that ever - all in all we are very happy!
However, the past few times we have gone on nights out with friends, he has been acting very different. The first incident was when he bumped into his prom date in a club and proceeded to flirt and spend all his time with her for the rest of the night. I'm not a jealous person, and I know he is really friendly so I just took this as him catching up with an old friend and didn't think much else of it.
The next time we went out we hadn't had sex for nearly a week (being the time of the month...) and while drunk in the taxi on the way home he totally embarrassed me in front of everyone (it was a 8 seater taxi) - telling them all how I don't put out, basically saying I'm a rubbish girlfriend for not providing him with enough sex. This really upset me as we do have a lot of sex and when we talked about it the next day he didn't remember a thing and apologized and I forgave him.
Now the third and most recent time is the worst of them all. We went to a friends birthday party and he ignored me the whole night. Every time I tried to talk to him or get a picture he wouldn't even look at me and would walk away. About an hour into the party, he became attached to this other girl and was literally joined to the hip with her all night. He had his arms round her and at one point he leaned in and kissed her on the cheek right in front of me. I was shocked and felt totally betrayed. He was very drunk and at the time was saying that it was okay because she knew I had a boyfriend but to me that's not okay. It's not okay how I had to spend the whole evening watching the love of my life stare in wonder at someone else and basically act single all night.
Yet again, he doesn't remember a thing but every time we kiss or get close all I can think about are these images in my head of him with his arms around this other woman. I'm trying to be brave and get over this but am really struggling! Is this normal? If anyone has any advice about how to forget this please help! I don't want to loose him, but I just don't understand why recently things like this keeps happening. I know he hasn't cheated so this probably sounds like nothing to worry about at all but I just feel so betrayed...