Boyfriend asked to go to a dance with another girl

yesterday one of my boyfriends good friends asked him to go to her ball for her sorority so he just kind of told me he was going & didn’t ask me. i’m not the jealous or controlling type but that one threw me off a little bit. i trust him but that’s like going to prom with another girl ... it just doesn’t happen. i told him that i wasn’t gonna tell him what to do, that it was his choice but i don’t feel 100% comfortable and it’s weird to me. he decided he wasn’t gonna go but i felt bad like i was holding him back from doing something fun with his friend bc he seemed excited. but it’s also another female and what if people get the wrong idea and i never have even met his friend in person. is me not wanting him to go okay ?