Should i really be mad at him?

This weekend I was hanging out with a bunch of people at my friends kickback. This guy that I really like was there and everyone went outside for a smoke. Me and him started makingout then later like 5 people left including me and him we went to walmart to eat. I was inside with everyone but him, his friend, and some girl. The next day I found out he was makingout with that girl in the car. Everyone was drunk that night so that's why I don't think I should get mad were not together but at the same time I still think that's shady.