Nude beach

So this past weekend my boyfriend went on a trip with a few of his other friends to the city, while they were there they went to a nude beach and they all stripped down. However he didn’t tell me about this and now days later I found out because one of his friends mentioned it. He thinks I’m overreacting for being annoyed and slightly upset that he didn’t tell me, but I know he would feel the same way if it was the other way around. This isn’t the first time he’s kept something (minor not major) from me and I just want everyone’s opinion.