The preview animation shows the Sim being desperate for a friend, though in game the Sim feels better alone.
Loner Sims will says the following when put into a rather large outing group: "This is more people than I can handle...I've got to get out of here!" followed by their feelings on the group outing. This occurs even with family members (tested with an 8-member group outing where 2 members were loners. After a few sim-minutes, both quit the group immediately leaving it a 6 member group).