You might try being honest. Try telling your manager how you feel. He might not realize that you feel the way you do.
Another possibility is that he might not be aware that you are being left out. Perhaps he thinks that someone else asked you to join them for drinks and you opted not to go. Miscommunication could be part of the problem.
Alternatively, they purposefully might not be inviting certain people. They may be unkind and inconsiderate.
Understandably, no one wants to be left out. It’s hurtful but, in reality, why should you want to be around people who are exclusionary and who don’t seem to want to be with you?
Ask yourself if these are really the people with whom you want to interact. Your time is better spent developing relationships with people who want to be with you and who would never exclude you from their group. Please take care.
Dr. Kristina Randle