Boyfriend’s friend question

If your boyfriend went out to dinner with his friend and her roommate without planning to tell you and then not invite you along once he does, how would you feel? She is my boyfriends ex girlfriend too but they weren’t that serious and I know he wouldn’t cheat. I’m really not trying to sound like I don’t want him hanging out with his friends. I feel like I’m getting unreasonably jealous so what are y’all’s opinions?