Boyfriend clubbing with a ex...

At first when he said he was going clubbing it was just a works thing, then he mentions my ex will be there, then to top it all he take a long one off he's mates, when it's only suppose to be a works thing. I don't care if he goes clubbing, I'm just mad that he's going clubbing with my ex? Someone who hurt me, and he doesn't see the problem with it. He told me that he wouldn't be with him, because there was 6 going so he'd be with everyone else to then wake up In the morning with them all arms around each other, in photos and laughing and talking in videos. Maybe I'm the only person who things this is just a little odd.