He’s better in one-on-one situations
Maybe in group settings he just takes over, dominating the situation, acting like this is his one-man show that everyone came here to watch. He’s pushy and bossy and not very personable. You say he’s better in one-on-one situations. Well, he’s an adult, he lives in the real world, and his social interactions cannot possibly be limited to one-on-one situations all of the time. So he needs to clean up his act and learn how to socialize without blowing up a social dynamic.