Group life is a delicate thing. You achieve a good balance and everyone seems to be enjoying one another's company and encouraging each other. Then the arrival of a new group member or the departure of an old one throws everything out of kilter.
I've been a part of Bible study groups (and other groups) of which my joy has quickly eroded after the arrival of a new person. Sometimes there has been a terrible personality clash. I remember being a part of one group where the arrival of a person with a sarcastic sense of humour, and the loss of several people with whom I got on very well quickly made the group pretty unbearable for me. I hate sarcasm, and now the group consisted mainly of sarcastic people who seemed to make me the butt of the jokes. I should have confronted them more and I didn't handle it very well. In the end, I eventually left. I have learned a lot from that experience.
This is a really difficult scenario of which I don't really have any answers. All I wish to say is that it happens. I've heard people say there are no such thing as 'personality clashes', and Christians should all just get along and be friends. I think we need to strive to live at peace with one another (I think some sarcastic people have 'issues' in their lives and look for a punching bag). But personality clashes DO exist. We can live at peace, but we can't be best friends with everyone. When I was at uni, the Christian group would hand out communication cards when setting up small groups for the year, and we were given the option of writing down on the card the name of anyone we didn't wish to be in a group with. Only the staffworkers would know about this and would do their best to accommodate everyone. I never wrote anyone's name down, but I can see that this is a great way to handle it. Everyone deserves the chance to study the Bible without being ridiculed and torn down. It would be awful if someone left a group because of this.
It's tricky because new people need to be welcomed into groups, and there is often no foreseeing what impact their arrival will have. At the same time, the leader has a responsibility to see that the existing group members are being taken care of.
Have you ever struggled in or left a group because of someone else that joined, or had the group's 'vibe' change?