Has your boyfriends friend ever done anything to you personally or said anything bad about you?
Are you friends with the friends girlfriend ?
Has your boyfriends friend ever tried to get your boyfriend to talk to other girls, get him to cheat or anything else seriously bad that’s risked your relationship?
If the answers no to all of them, then I don’t see what your personal problem is with this friend. He might be a crappy or bad guy, or lack morals in your eyes but it’s kinda nothing to do with you? Even if you’re friends with the girlfriend, it’s still nothing to do with you but you gotta back a friend so understandable.
If you’re annoyed at your boyfriend for leaving you to go meet his friends and you had other plans or thought you’d both be doing something else, or he’s left you without saying anything then you have every right to be upset and should defo tell him what you’re feeling and thinking. And why.
Otherwise, wait until you are alone with your boyfriend next and tell him how you feel about his friend and why and what you want him to do I.e. not hang around with him.
You have to remember tho, if you have no serious personal reasons to not like this friend then it’s really unreasonable to ask him to stop seeing a friend and that he might not agree with you and might not stop hanging around with him.
If they’re not really close, he might be alright with it but otherwise you’ll just need to accept it and get over it (even if you don’t like it)