What is the relationship between Hermia and Helena? How does Helena betray the secret Hermia tells her?
Helena and Hermia have been friends since they were little kids.
As far as the secret goes, you can find this in the first scene of the play. The secret that Hermia tells her is that Hermia is going to run away with Lysander. Hermia does not want to marry Demetrius, but she has to.
Helena is in love with Demetrius. But weirdly, she decides that she should tell him Hermia's secret. She thinks that he will think better of her if she does. She also figures that it will give her an excuse to talk to him a couple of times.