Most Helpful Guy
Maybe stop having him do it in front of other people, thats probably awkard as fuck for him to be kissing his girlfriend in front of other people because they're telling him to. Talk to him about it alone with just you and him and I'm sure he'll want to kiss you, if not then you got some figuring out to do.
Most Helpful Girl
Maybe he is shy. Maybe he doesn't know how to kiss and gets nervous. Maybe he doesn't like anyone to be around. Etc.
There isn't enough information here to conclude anything. Just guesses. You must confront him and ask him about it.