By the end of Act 2 of A Midsummer Night's Dream, what is similar about the pairs (Lysander-Hermia, Demetrious-Helena, and Oberon-Titania)?
By the end of Act 2, the lovers are all fighting and confused, and matched up with the wrong lover.
The main problem is that Puck and Oberon were trying to fix the lovers’ quarrel, possibly because Oberon was sympathetic, having experienced a severe fight with his own lover Titania. As a result, Lysander and Hermia are not together, and Demetrius and Lysander are both looking for Helena. Helena is annoyed and confused, because she thinks they are all three making fun of her.
Do not say so, Lysander; say not so.
What though he love your Hermia?(110)
Lord, what though?
Yet Hermia still loves you; then be content. (Act 2, Scene 2)
Therefore at the end of Act 2, everything is a mess. Oberon has not gotten back together with Titania, and all four of the young lovers are mixed up, with both men after Helena instead of Hermia.
The three pairs of Lysander-Hermia, Demetrius-Helena and Oberon-Titania are similar in the sense that they are not together as they should, and something keeps them apart from each other.
Lysander and Hermia are in love but can’t be together, because Hermia’s father does not approve of their relationship, and instead wants Hermia to marry Demetrius. Lysander devises a way that they would be together far from the laws of Athens that would hinder their union.
Demetrius and Helen are not truly together because Demetrius loves Hermia and wants to marry her. Helen feels rejected but continues to pursue Demetrius.
Oberon and Titania are also estranged because of a dispute between them. They both want to keep a boy who lost his mother at birth. Oberon wants the boy for his attendant while Titania wants to raise the boy.