In the introduction to the Arden edition of A Midsummer Night's Dream, the editor, Harold Brooks, argues that the theme of the play is love consummated in marriage:
Love and marriage is the central theme: love aspiring to and consummated in marriage, or to a harmonious partnership within it. Three phases of this love are depicted: its renewal, after a breach, in the long-standing marriage of Oberon and Titania; adult love between mature people in Theseus and Hippolyta; and youthful love with its conflicts and their resolution, so that stability is reached, in the group of two young men and two girls. (Brooks 1979: cxxx)
Marriage is both society's acknowledgement of and its leashing of individual passion. In A Midsummer Night's Dream, love is easily swayed but indisputable when felt. Hermia and Lysander risk death and shame by eloping rather than obeying Theseus and Hermia's father, and accepting that Hermia marry Demetrius, whom she does not love.
The young women are constant to their lovers, but the men are constant to each other.