Theseus gives Hermia 3 options, but none of them include marrying Lysander. Hermia only wants to marry Lysander so she doens't choose any of the options from Theseus.
Act III: Climax
I love her more!
Since Hermia isn't allowed to marry Lysander, they run away into the forrest to be together. Before she runs away she tells Helena about their plan. Helena tells Demetrius about the plan and they all run into the woods.
Act IV: Falling Action
Three way wedding!
Oberon sees how much Helena loves Demetrius, but he doesn't love her back. Oberon tells his fairy assistant, Puck, to drop love potion in Demetrius's eyes so he loves Helena. Puck accidently puts it in Lysander's eyes, so he loves Helena.
Act V: Resolution
Puck tries to fix everything by putting potion in Demetrius's eyes, but it makes everything worse because Lysander and Demetrius love Helena. They want to fight over her, and Hermia is so confused on what's going on.
That didn't help.
They all fall asleep and Puck reverses the potion. They all wake up and think it was a dream. Theseus shows up and they tell him what happened. Theseus says to have a triple wedding.
The 3 couples get married and the rustics preform their play at the wedding. Puck closes off the play by telling everyone if you didn't like it act like it was a dream.