Chagiga 11B - Why Can't עריות (forbidden relationships) be taught to more than two people?

Chagiga 11b

1. Gemara's analysis as to why עריות, forbidden sexual relationships, should not be taught to more than two people at once.
2. A discussion about the proper pedagogical methods to prevent students from getting distracted.
3. Discussion about the meaning of the "Secrets of Forbidden Relationships." Is this referring to Halachic points, or spiritual secrets?