In Act 3, Scene 2, Helena accuses Hermia of conspiring with both Lysander and Demetrius in mocking her. In other words, Helena does not believe that either Lysander or Demetrius are being sincere when they proclaim they love her. Helena believes they are both doing it to mock her, meaning to make fun of her in a very hateful and mean-spirited manner. Furthermore, Helena believes that Hermia is in on the joke and is also making fun of her, as we see in Helena's lines:
Lo, she is one of this confederacy!
Now I perceive they have conjoin'd all three
To fashion this false sport, in spite of me. (III.ii.195-197)
Not only does Helena accuse Hermia of conspiring with Lysander and Demetrius to hatefully make fun of her, she also accuses Hermia of forgetting their childhood friendship. She demands of Hermia how she could have forgotten all the hours they spent together sharing everything, "As if our hands, our sides, voices, and minds / Had been incorporate" (210-211). At the end of her accusation speech, Helena asks Hermia how she could allow herself to break up their precious friendship "[t]o join with men in scorning [her] poor friend?" (219). By "scorn," Helena means showing contempt or hatred. Therefore, Helena is accusing Hermia of joining forces with both the men to mock Helena, thereby showing Helena hatred and contempt and breaking up their friendship.