I think the slow opening scene does you a disservice, mainly because it breaks the show-not-tell rule. One character is telling us what the other character is like instead of that character demonstrating those attribute and it felt to me that your forcing me to think what this character is like (instead of showing). Which is really strange because, to my surprise, the rest of the episode not only does the opposite, but it does it really, really well.
The therapist is great (love the bit where he methodically counts five attendees) and I dispute what others have said about not explaining enough about what is going on. You’ve created this strange, awkward, but not unbelievable, situation. You’ve established personalities for all the characters and that they are attending a therapy session. I don’t know why they are there, but I do want to know. And you did all that in a very short space of time.
I did like the bit where the therapist asks them to make up pairs and doesn’t seem to have realised five is an odd number. I felt a nice comic moment was lost when the therapist didn’t seem surprised that one person didn’t have a partner.
It’s hard to say, but I think if you took out that opening scene and get straight into the students entering the hall, it would still come over that that those two characters know each other when the guy turns up late. So maybe take it out?